Slow Cooker Sourdough Discard Spiced Apple Cider Custard Tart

Name: Slow Cooker Sourdough Discard Spiced Apple Cider Custard Tart
Prep time: 25 min
Total time: 25 min
Yield: 6 servings
Cuisine: American
Ingredients: 1 cup (240 ml) active sourdough starter discard, at room temperature, bubbly; 4 tablespoons (57 g) unsalted butter, softened, softened to room temperature; 3 tablespoons (38 g) granulated sugar; ½ cup (60 g) all-purpose flour; ¼ teaspoon (1½ g) fine sea salt; ¼ teaspoon (1¼ g) baking soda; 5 medium (800 g) Honeycrisp or Granny Smith apples, peeled and cored, peeled, cored, sliced ¼ inch thick; 1 cup (240 ml) fresh apple cider (not juice); 1½ teaspoon (3¾ g) ground cinnamon; ¼ teaspoon (½ g) freshly grated nutmeg; 3 tablespoons (38 g) granulated sugar; 1 tablespoon (8 g) cornstarch; 1 tablespoon (15 ml) fresh lemon juice; 3 large eggs; ¼ cup (50 g) granulated sugar; ¾ cup (180 ml) heavy cream; 1 teaspoon (5 ml) vanilla extract; ⅛ teaspoon (¾ g) fine sea salt

From the MyKitchenBank Kitchen

A unique dessert that transforms sourdough starter discard into a tender crust, topped with cinnamon-spiced apples cooked in apple cider, then finished with a silky custard layer—all gently cooked in a slow cooker. The result is a warm, comforting tart with complex flavors and minimal active cooking time.

Prep: 25 min
Cook: —
Wait: 3 hr
Total: 3 hr 25 min
Makes: 1 tart (6 slices)

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Ingredients

6 servings

For the crust
1 cup (240 ml) active sourdough starter discard, at room temperature, bubbly
4 tablespoons (57 g) unsalted butter, softened, softened to room temperature
3 tablespoons (38 g) granulated sugar
½ cup (60 g) all-purpose flour
¼ teaspoon (1.5 g) fine sea salt
¼ teaspoon (1.3 g) baking soda
For the filling
5 medium (800 g) Honeycrisp or Granny Smith apples, peeled and cored, peeled, cored, sliced ¼ inch thick
1 cup (240 ml) fresh apple cider (not juice)
1½ teaspoon (3.8 g) ground cinnamon
¼ teaspoon (0.5 g) freshly grated nutmeg
3 tablespoons (38 g) granulated sugar
1 tablespoon (8 g) cornstarch
1 tablespoon (15 ml) fresh lemon juice
For the custard
3 large eggs
¼ cup (50 g) granulated sugar
¾ cup (180 ml) heavy cream
1 teaspoon (5 ml) vanilla extract
⅛ teaspoon (0.8 g) fine sea salt

Equipment (11)

6-quart (5.7 L) slow cooker
6-inch (15 cm) round cake pan or similar insert that fits in your slow cooker
Parchment paper
Medium mixing bowl
Large mixing bowl
Whisk
Wooden spoon
Measuring spoons and cups
Sharp knife
Cutting board
Kitchen towel or foil

Steps

Before you start

Have sourdough discard at room temperature (active and bubbly is ideal)
Peel and slice apples just before assembly so they don't brown
Line your slow cooker with parchment paper for easy removal
Set up a slow cooker with a 6-inch round or similar-sized insert or cake pan that fits inside

1
Mix crust dough
- In a medium bowl, whisk together the sourdough discard, softened butter, and 3 tablespoons sugar until well combined and smooth.
- In a separate small bowl, mix the ½ cup flour, salt, and baking soda.
- Fold the dry ingredients into the wet ingredients until just combined—don't overmix.
- The dough will be thick and slightly sticky.
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Ready when: dough is thick and combined, slightly sticky
Tip: Don't overwork the dough; gentle folding prevents a tough crust.
2
Prepare slow cooker and press crust
- Line a 6-inch (15 cm) round cake pan with parchment paper.
- Press the sourdough dough evenly into the bottom of the pan, covering it in a thin layer about ⅛ to ¼ inch thick.
- Place a piece of parchment paper at the bottom of your slow cooker, then set the cake pan on top.
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Ready when: dough is evenly distributed across the pan bottom
Tip: Parchment paper prevents sticking and makes removal easier.
3
Prepare apple filling
- In a large bowl, combine the sliced apples, 1 cup apple cider, cinnamon, nutmeg, 3 tablespoons sugar, cornstarch, and lemon juice.
- Stir gently until the apples are evenly coated and the cornstarch is fully dissolved.
- Let sit for 2 minutes to allow the cornstarch to hydrate.
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Ready when: apples are coated and mixture is slightly thickened
Tip: Use fresh apple cider (not juice) for deeper, tannic flavor that complements the spices.
4
Layer apples onto crust
- Pour the apple mixture (apples and cider sauce) evenly over the sourdough crust in the cake pan.
- Arrange any excess apples in an even layer.
- The mixture should come about ¾ of the way up the sides of the pan.
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Ready when: apples are evenly layered
Tip: Don't pack the apples tightly; they'll release liquid as they cook.
5
Make custard mixture
- In a medium bowl, whisk together the 3 eggs and ¼ cup sugar until pale and slightly thickened, about 2 minutes of whisking.
- Pour in the heavy cream, vanilla extract, and salt, and whisk gently until just combined.
- The mixture should be smooth and uniform.
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Ready when: custard is pale, smooth, and uniform
Tip: Whisk gently when adding cream to avoid incorporating too much air, which can cause bubbles in the final custard.
6
Pour custard and cover slow cooker
- Carefully pour the custard mixture over the apple layer, distributing it evenly.
- The custard will settle and fill the gaps.
- Cover the slow cooker with a damp kitchen towel (to absorb condensation and prevent water droplets from falling onto the tart), then place the lid on top, leaving it slightly ajar—about ½ inch of gap—to allow steam to escape.
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Ready when: custard is evenly distributed
Tip: A slightly ajar lid prevents custard curdling from excess steam condensation dripping back into the tart.
7
Cook on low
- Turn the slow cooker to LOW and cook for 2½ to 3 hours.
- The tart is done when the custard is set around the edges but still has a slight jiggle (about ½ inch) in the very center when you gently shake the pan.
- The apples should be tender and the crust should be set and slightly firmer at the edges.
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Ready when: custard is set at edges with slight center jiggle (½ inch); apples are tender
Tip: Don't cook it too long—overcooking will cause the custard to curdle and separate. Check around 2½ hours.
8
Cool in slow cooker
- Turn off the slow cooker and leave the tart inside with the lid ajar for 30 minutes.
- This gradual temperature drop prevents the custard from cracking.
- After 30 minutes, carefully remove the cake pan from the slow cooker and set it on a wire rack to cool to room temperature, about 1 hour.
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Ready when: tart is cool to the touch and no longer steaming
Tip: Gradual cooling prevents the custard from contracting too quickly and cracking.
9
Chill and unmold
- Once cooled, refrigerate the tart in its pan for at least 2 hours, or up to 8 hours, until the custard is fully set and chilled.
- To unmold, run a thin knife around the edge of the pan, then carefully invert onto a serving plate.
- Peel away the parchment paper.
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Ready when: custard is firm and doesn't jiggle when pan is shaken
Tip: Chilling makes the tart much easier to unmold and slice cleanly.

Good to know

Tips

Sourdough discard should be bubbly and active (fed within 4–8 hours) for the best rise and tangy flavor in the crust. If your starter is sluggish, add ¼ teaspoon baking powder to boost lift.
The slow cooker's gentle, even heat is key—it prevents the custard from curdling or the crust from browning too much. Do not use HIGH heat.
If your slow cooker runs hot, check the tart at 2 hours 15 minutes instead of 2½ hours. Slow cookers vary widely in temperature.
For the cleanest slices, chill the tart thoroughly (at least 4 hours) before serving. A hot tart will be too soft to slice neatly.

Make ahead

Assemble the tart up to 4 hours ahead, refrigerate it covered, then slow-cook it when ready (timing may increase by 15–20 minutes if starting from cold). Do not prepare the components more than 4 hours in advance, as the apples will brown.

Storage & reheating

Store covered in the refrigerator for up to 3 days. Serve chilled or at room temperature. To reheat, place a slice on a plate and warm gently in a 300°F (150°C) oven for 10–12 minutes until warmed through. The tart does not freeze well due to the custard's texture.

Substitutions

Honeycrisp or Granny Smith apples, peeled and cored → Pears or a mix of apples and pears (about 5 medium fruits). Pears will be slightly softer and more delicate; reduce cooking time by 15 minutes if using mostly pears.
fresh apple cider (not juice) → Unsweetened apple juice mixed with 1 tablespoon of apple cider vinegar. Cider provides deeper flavor, but juice with a touch of vinegar approximates its tannic quality.
ground cinnamon → Ground cardamom or allspice (use same amount). Cardamom adds a more floral note; allspice is warmer and slightly more peppery.
vanilla extract → Almond extract or bourbon (use ½ teaspoon of almond extract or 1 teaspoon bourbon). Almond adds nuttiness; bourbon adds warmth and depth.