CakesAmericanMedium

Slow Cooker Rhubarb and Strawberry Custard Cake with Meringue

Name: Slow Cooker Rhubarb and Strawberry Custard Cake with Meringue
Prep time: 25 min
Cook time: 1 h 15 min
Total time: 1 h 40 min
Yield: 8 servings
Cuisine: American
Ingredients: 6 tablespoons (85 g) unsalted butter, softened, softened to room temperature; ¾ cup (150 g) granulated sugar; 3 large eggs, separated (yolks and whites kept separate, both at room temperature); 1 cup (120 g) all-purpose flour; 3 tablespoons (25 g) custard powder (Bird's or equivalent); 1 teaspoon (5 g) baking powder; ¼ teaspoon (1½ g) fine sea salt; ¾ cup (180 ml) whole milk; 1 teaspoon (5 ml) vanilla extract; 8 ounces (225 g) fresh rhubarb, trimmed, cut into ½-inch (1.25 cm) pieces; 8 ounces (225 g) fresh strawberries, hulled, quartered; ½ teaspoon (2 g) lemon zest, finely grated; 1 large egg white (reserved from the cake), at room temperature (reserved from the 3 eggs above); ¼ teaspoon (1 g) cream of tartar; 6 tablespoons (75 g) granulated sugar (for meringue); ¼ teaspoon (1¼ ml) vanilla extract (for meringue); ½ teaspoon (2½ g) cornstarch (for meringue stability)

From the MyKitchenBank Kitchen

A tender, custardy cake studded with tart rhubarb and sweet strawberries, baked gently in a slow cooker, then topped with a toasted meringue. The slow, moist heat creates a cake-and-custard hybrid with a luscious center, while the meringue adds dramatic finish with a crispy, golden exterior and soft, marshmallow interior.

Prep: 25 min
Cook: 1 hr 15 min
Wait: 45 min
Total: 2 hr 25 min
Makes: 1 cake (8 servings)

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Ingredients

8 servings

For the cake
6 tablespoons (85 g) unsalted butter, softened, softened to room temperature
¾ cup (150 g) granulated sugar
3 large eggs, separated (yolks and whites kept separate, both at room temperature)
1 cup (120 g) all-purpose flour
3 tablespoons (25 g) custard powder (Bird's or equivalent)
1 teaspoon (5 g) baking powder
¼ teaspoon (1.5 g) fine sea salt
¾ cup (180 ml) whole milk
1 teaspoon (5 ml) vanilla extract
8 ounces (225 g) fresh rhubarb, trimmed, cut into ½-inch (1.25 cm) pieces
8 ounces (225 g) fresh strawberries, hulled, quartered
½ teaspoon (2 g) lemon zest, finely grated
For the meringue topping
1 large egg white (reserved from the cake), at room temperature (reserved from the 3 eggs above)
¼ teaspoon (1 g) cream of tartar
6 tablespoons (75 g) granulated sugar (for meringue)
¼ teaspoon (1.3 ml) vanilla extract (for meringue)
½ teaspoon (2.5 g) cornstarch (for meringue stability)

Equipment (10)

6–7-quart slow cooker
9-inch (23 cm) round cake pan or 2-quart soufflé dish (must fit inside slow cooker)
Parchment paper
Large mixing bowl
Medium mixing bowl
Whisk
Electric mixer (handheld or stand)
Cutting board and knife
Measuring cups and spoons
Instant-read thermometer

Steps

Before you start

Slow cooker must be at least 6 quarts; a 7-quart oval works best. Line the bottom and lower sides with parchment paper for easy removal.
Have all ingredients measured and at room temperature before starting (eggs, milk, custard powder).
Prepare a 9-inch (23 cm) round cake pan that fits inside your slow cooker, or use a soufflé dish.
Preheat your slow cooker on LOW for 5 minutes while you assemble the batter.

1
Prepare slow cooker
- Turn slow cooker to LOW and let it preheat for 5 minutes.
- Tear off a long sheet of parchment paper and line the bottom and lower 2 inches (5 cm) of the sides of a 9-inch (23 cm) round cake pan or 2-quart soufflé dish.
- The paper will help you lift the finished cake out.
- Place a sturdy wire rack or crumpled foil balls on the bottom of the slow cooker to keep the pan elevated and prevent direct heat contact with the base (this prevents overbrowning the bottom).
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Tip: The rack or foil balls are essential—they allow steam to circulate and keep the bottom of the cake from overcooking.
2
Cream butter and sugar
- In a large bowl, beat together softened butter and the 0.75 cup (150 g) granulated sugar with an electric mixer on medium speed for 2–3 minutes, until the mixture is pale, fluffy, and light in color.
- Scrape down the bowl halfway through.
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Ready when: Mixture is pale, fluffy, and increased in volume by about one-third
Tip: Creaming butter and sugar introduces air, giving the cake a lighter crumb. Don't skip this step.
3
Add egg yolks
- Add the 3 egg yolks to the butter mixture one at a time, beating well after each addition (about 30 seconds per yolk).
- The mixture may look slightly broken—this is normal.
- Beat in the vanilla extract (1 teaspoon / 5 ml) until combined.
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Ready when: All yolks are incorporated and mixture is well combined
Tip: Add yolks slowly so the mixture emulsifies smoothly. Slightly broken-looking is fine—don't overmix.
4
Combine dry ingredients
- In a medium bowl, whisk together the all-purpose flour (1 cup / 120 g), custard powder (3 tablespoons / 25 g), baking powder (1 teaspoon / 5 g), and fine sea salt (0.25 teaspoon / 1.5 g) until well combined with no lumps.
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Ready when: No lumps visible, custard powder fully distributed
Tip: Whisking the dry ingredients ensures the baking powder and custard powder are evenly distributed, preventing dense patches.
5
Build the batter
- Add the dry mixture (in two additions) to the butter mixture, alternating with the milk (0.75 cup / 180 ml).
- Start and end with the dry ingredients.
- After each addition, stir gently with a rubber spatula until just combined—do not overmix.
- The batter will be thick but pourable.
- Fold in the rhubarb pieces (8 oz / 225 g), strawberry quarters (8 oz / 225 g), and lemon zest (0.5 teaspoon / 2 g) with a few gentle strokes until evenly distributed.
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Ready when: Batter is smooth with no streaks of dry flour, fruit is distributed throughout
Tip: Overmixing develops gluten and makes the cake tough. Stop as soon as you see no dry flour.
6
Transfer to slow cooker
- Scrape the batter into the prepared 9-inch (23 cm) cake pan or soufflé dish.
- Smooth the top.
- Carefully place the pan on the wire rack or foil balls inside the preheated slow cooker.
- If needed, use foil strips as handles to help lower the pan safely.
- Cover the slow cooker with the lid.
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Ready when: Pan is level and stable in the slow cooker
Tip: Keep the pan elevated; if it touches the bottom, the cake will brown too much on the underside.
7
Bake the cake (low heat)Oven 212°F / 100°C
- Cook on LOW for 2 hours to 2 hours 15 minutes.
- The cake is done when a toothpick inserted in the center comes out with just a few moist crumbs (not wet batter).
- The edges should pull slightly away from the pan sides, and the top will look set and slightly domed.
- The internal temperature at the center should reach 210–212°F (99–100°C).
- Do not peek frequently; this releases steam and extends cooking time.
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Ready when: Toothpick emerges with just a few moist crumbs, edges pull slightly from sides, top is set and domed
Tip: Slow cookers vary; check at 2 hours. The cake will seem slightly custardy on top—that's intentional and cooks through. The residual heat will firm it up a bit as it cools.
8
Cool the cake
- Carefully lift the pan out of the slow cooker using foil strip handles or tongs.
- Turn off the slow cooker.
- Let the cake rest in the pan at room temperature for 15 minutes, then run a thin knife around the edge to loosen it.
- Invert onto a wire rack and peel off the parchment paper, then invert again so the top is facing up.
- Let cool to room temperature, about 20–25 minutes, before topping with meringue.
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Ready when: Cake is loosened from pan and cooled to room temperature (warm to the touch but not hot)
Tip: While still slightly warm, the cake will accept the meringue without causing it to deflate. Don't let it cool completely.
9
Make the meringue
- In a very clean medium bowl, beat the reserved egg white (1 large / room temperature) with cream of tartar (0.25 teaspoon / 1 g) on medium-high speed with an electric mixer for about 1 minute until soft peaks form.
- Gradually add the 6 tablespoons (75 g) sugar while continuing to beat, about 1 tablespoon every 15 seconds.
- Once all sugar is added, continue beating for 2–3 minutes more until stiff, glossy peaks form and the sugar is dissolved (rub a tiny amount between your fingers—it should feel smooth, not grainy).
- Beat in the vanilla extract (0.25 teaspoon / 1.25 ml).
- Sift the cornstarch (0.5 teaspoon / 2.5 g) over the meringue and fold it in gently with just 3–4 strokes.
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Ready when: Meringue holds stiff, glossy peaks; sugar is fully dissolved and not grainy; cornstarch is barely folded in
Tip: Even a speck of yolk or fat will prevent proper whipping. Use a spotlessly clean bowl and beaters. The cornstarch stabilizes the meringue and helps it brown beautifully.
10
Spread meringue and toastOven 425°F / 220°C
- Preheat the oven to 425°F (220°C).
- Spread the meringue over the warm cake, starting from the center and working outward, creating peaks and swirls with the back of a spoon or an offset spatula.
- Make sure the meringue reaches the edges of the cake and completely covers it (this seals in the cake and prevents the meringue from shrinking away).
- Place the cake on a baking sheet and bake at 425°F (220°C) for 8–10 minutes, until the meringue is golden brown on the peaks and pale golden on the sides.
- Watch carefully—meringue browns quickly.
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Ready when: Meringue peaks are golden brown, sides are pale golden, and the meringue feels firm to a light touch
Tip: Don't touch the hot oven door during baking—meringue can fall if jostled. High heat gives you a crispy outside and soft inside.
11
Cool and serve
- Let the cake cool at room temperature for at least 10 minutes before slicing (meringue will firm up as it cools).
- Serve warm or at room temperature.
- A thin, sharp knife dipped in hot water and wiped between cuts will give you clean slices.
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Ready when: Meringue is set and no longer sticky to the touch
Tip: Hot-knife slicing is the secret to beautiful, neat servings without the meringue cracking or dragging.

Good to know

Tips

Separate your eggs when they're cold (fresher eggs separate cleanly), but bring both yolks and whites to room temperature before mixing. Room-temperature egg whites whip to superior volume and stability.
If your slow cooker runs very hot, start checking the cake at 1 hour 45 minutes. Some slow cookers can finish the cake faster. You're aiming for that sweet spot where the edges and middle are set but still custardy beneath the surface.
The meringue must be spread on a warm (not hot) cake, or the heat will cook the underside and make it tough. Conversely, a completely cool cake won't allow the meringue to adhere and set properly.
For best meringue texture, use a high-protein egg white (pastured or farm-fresh eggs often have whippier whites). Avoid old eggs; whites from eggs past their prime won't whip as stiffly.

Make ahead

The cake (without meringue) can be baked up to 1 day ahead, wrapped tightly, and stored at room temperature. Make and toast the meringue no more than 2–3 hours before serving for best crispness. Do not refrigerate the finished cake once meringue is applied—the cold will weep moisture and make the meringue sticky.

Storage & reheating

**Room temperature (up to 4 hours)**: Cover loosely with a cake dome or large bowl. The meringue will gradually soften. | **Refrigerator (up to 2 days)**: Transfer to an airtight container. The meringue will weep and become sticky—this is normal and doesn't affect flavor. Let come to room temperature before serving. | **Freezer (up to 1 month)**: Wrap the unmeringued cake tightly in plastic wrap and foil. Thaw at room temperature, then apply fresh meringue and toast before serving. Do not freeze the meringued cake—the moisture from thawing will ruin the topping.

Substitutions

custard powder (Bird's or equivalent) → vanilla pudding powder or instant vanilla dessert mix (use the same amount, 3 tablespoons / 25 g). Provides the same custardy flavor and texture. Bird's custard powder is traditional, but this works well as an alternative.
fresh rhubarb, trimmed → 8 oz (225 g) frozen rhubarb, thawed and drained (squeeze gently to remove excess liquid). Works in a pinch, though fresh has better texture. Reduce liquid slightly as thawed rhubarb releases extra moisture.
fresh strawberries, hulled → 8 oz (225 g) frozen strawberries, thawed and drained (squeeze gently). Acceptable substitute. Frozen fruit will release more liquid, so don't add extra milk to the batter.
lemon zest → 0.5 teaspoon (2.5 ml) fresh lemon juice mixed into the batter, or 0.125 teaspoon (0.5 g) ground dried lemon zest. Lemon juice adds brightness; dried zest is more muted. Either complements the rhubarb and strawberry well.