Slow Cooker Brunch Frittata with Sautéed Mushrooms and Gruyère

Name: Slow Cooker Brunch Frittata with Sautéed Mushrooms and Gruyère
Prep time: 15 min
Cook time: 25 min
Total time: 40 min
Yield: 6 servings
Cuisine: French
Ingredients: 10 large large eggs, at room temperature; 12 oz (340 g) mixed fresh mushrooms (cremini, oyster, shiitake), cleaned and sliced ¼ inch thick; 2 medium (80 g) shallots, thinly sliced; 1½ cups (150 g) Gruyère cheese, finely grated; 1 tablespoon (3 g) fresh thyme, leaves only, roughly chopped; 2 tablespoons (28 g) unsalted butter, cold; ½ tablespoon (7 g) unsalted butter, softened; ½ cup (120 ml) heavy cream; 1 teaspoon (6 g) kosher salt; ½ teaspoon (1 g) freshly ground black pepper; ⅛ teaspoon (½ g) freshly grated nutmeg; ¼ cup (25 g) Parmigiano-Reggiano cheese, finely grated (optional)

From the MyKitchenBank Kitchen

A French-inspired frittata gently cooked in a slow cooker, featuring tender sautéed mushrooms and creamy Gruyère cheese. This hands-off method is perfect for weekend brunch, yielding a custardy center with set edges. The frittata is finished under the broiler for a golden top.

Prep: 15 min
Cook: 25 min
Wait: 1 hr 40 min
Total: 2 hr 20 min
Makes: 1 frittata (6 slices)

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Ingredients

6 servings

10 large large eggs, at room temperature
12 oz (340 g) mixed fresh mushrooms (cremini, oyster, shiitake), cleaned and sliced ¼ inch thick
2 medium (80 g) shallots, thinly sliced
1½ cups (150 g) Gruyère cheese, finely grated
1 tablespoon (3 g) fresh thyme, leaves only, roughly chopped
2 tablespoons (28 g) unsalted butter, cold
½ tablespoon (7 g) unsalted butter, softened
½ cup (120 ml) heavy cream
1 teaspoon (6 g) kosher salt
½ teaspoon (1 g) freshly ground black pepper
⅛ teaspoon (0.5 g) freshly grated nutmeg
¼ cup (25 g) Parmigiano-Reggiano cheese, finely grated (optional)

Equipment (10)

6-quart slow cooker
Large skillet (10-inch/25 cm)
Medium mixing bowl
Whisk
Cutting board
Chef's knife
Box grater or microplane
Wooden spoon
Silicone spatula
Shallow baking dish or pie plate that fits inside slow cooker (if not using slow cooker insert directly)

Steps

Before you start

Preheat your slow cooker on low for 10 minutes if your model requires it
Line a 6-quart slow cooker with parchment paper or use a slow cooker liners for easy removal
Have your broiler rack positioned 6 inches from the heating element and preheat broiler just before finishing
Bring eggs to room temperature for the most even cooking

1
Sauté mushrooms and shallots
- Heat 2 tablespoons (28 g) unsalted butter in a large 10-inch (25 cm) skillet over medium-high heat.
- Once foaming, add the sliced shallots and cook for 1 minute until fragrant.
- Add the sliced mushrooms and cook, stirring occasionally with a wooden spoon, for 6–8 minutes.
- The mushrooms will first release their liquid, then it will evaporate and they'll turn golden.
- Season with a pinch of salt and pepper, then remove from heat and let cool slightly.
- Stir in the chopped fresh thyme.
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Ready when: Mushrooms are tender and golden, liquid has mostly evaporated
Tip: Do not crowd the pan; let mushrooms brown rather than steam. This concentrates their flavor.
2
Prepare slow cooker
- While mushrooms cook, butter the inside of a 6-quart slow cooker generously with the 0.5 tablespoon (7 g) softened butter, especially the bottom and corners.
- You can also line it with parchment paper for easier removal.
3
Whisk egg custard
- In a medium mixing bowl, whisk together the 10 large eggs at room temperature, 0.5 cup (120 ml) heavy cream, 1 teaspoon (6 g) kosher salt, 0.5 teaspoon (1 g) freshly ground black pepper, and 0.125 teaspoon (0.5 g) freshly grated nutmeg.
- Whisk for about 30 seconds until the mixture is light and homogeneous with a consistent pale color.
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Ready when: Eggs are fully incorporated and slightly frothy
Tip: Room-temperature eggs mix more evenly and cook more uniformly in the slow cooker.
4
Layer frittata in slow cooker
- Pour one-third of the egg mixture into the prepared slow cooker.
- Scatter half of the cooled sautéed mushroom mixture over the egg layer.
- Sprinkle with half of the grated Gruyère (about 0.75 cup/75 g).
- Pour another third of the egg mixture over the cheese.
- Layer the remaining mushrooms and the remaining Gruyère cheese.
- Pour the final third of the egg mixture on top, making sure to cover all the cheese and mushrooms evenly.
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Ready when: All ingredients are evenly distributed in layers
Tip: Layering helps distribute the mushrooms and cheese evenly throughout the frittata, preventing them from settling to the bottom.
5
Cook in slow cooker
- Cover the slow cooker and cook on low for 1 hour 20 minutes to 1 hour 40 minutes (80–100 minutes total).
- The edges of the frittata will set and pull slightly away from the sides of the slow cooker, but the center will still have a slight jiggle when you gently shake the slow cooker.
- Do not overcook or the eggs will become rubbery.
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Ready when: Edges are set and pull away from the sides; center has a slight jiggle but is mostly set
Tip: Slow cookers vary in temperature; start checking at 80 minutes. The carryover heat will continue cooking the center even after you remove it from the slow cooker.
6
Finish under the broilerOven 500°F / 260°C
- Turn on your broiler and position the rack 6 inches (15 cm) from the heating element.
- Carefully remove the slow cooker insert or transfer the frittata to a shallow baking dish that will fit under your broiler.
- If using the optional Parmigiano-Reggiano, sprinkle the 0.25 cup (25 g) grated cheese evenly over the top of the frittata.
- Place under the broiler for 3–5 minutes, watching carefully, until the top is lightly golden and any exposed egg is set.
- The cheese should be bubbling and light golden.
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Ready when: Top is light golden, cheese is bubbling, any visible egg is set
Tip: Watch constantly under the broiler—it can go from golden to burnt in seconds. If your broiler is very hot, start checking after 2 minutes.
7
Rest and serve
- Remove the frittata from the broiler and let it rest for 5 minutes.
- This allows the center to firm up slightly and makes slicing easier.
- Cut into 6 wedges and serve warm or at room temperature.
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Ready when: Frittata is stable enough to cut cleanly
Tip: A hot, sharp knife dipped in water between cuts helps create clean slices without dragging the eggs.

Good to know

Tips

The slow cooker's gentle, even heat produces a custard-like center that's impossible to achieve on the stovetop. Don't skip the broiler finish—it adds essential color and sets the top perfectly.
For a vegetarian-friendly brunch, add sautéed spinach or leeks alongside the mushrooms. Reduce the mushroom quantity slightly if adding extra vegetables.
This frittata is excellent served with crusty bread, a simple green salad, or a glass of sparkling wine for a classic French brunch spread.
Make it a day ahead and serve it at room temperature. It's just as delicious cold or reheated and makes a great make-ahead dish for entertaining.

Make ahead

You can sauté the mushrooms and shallots up to 8 hours ahead. Store them in an airtight container in the refrigerator. Let them come to room temperature before layering into the slow cooker. You can also whisk the egg mixture up to 4 hours ahead and refrigerate it in a covered bowl.

Storage & reheating

Store leftovers in an airtight container in the refrigerator for up to 3 days. Reheat individual slices in a 300°F (150°C) oven for 8–10 minutes until warmed through, or reheat in the microwave at 50% power for 60–90 seconds. The frittata can be frozen for up to 1 month; thaw overnight in the refrigerator before reheating.

Substitutions

Gruyère cheese → Emmental or Swiss cheese. Both have a similar nutty, mild flavor and melt beautifully. Use the same quantity.
mixed fresh mushrooms (cremini, oyster, shiitake) → Baby bella mushrooms or cremini only. If you can't find a mix, cremini or baby bella mushrooms work perfectly. Use the same total weight.
fresh thyme → Dried thyme. Use 1 teaspoon (1 g) dried thyme instead of fresh. It has a more concentrated flavor.
heavy cream → Whole milk or crème fraîche. Milk will result in a slightly thinner custard; crème fraîche adds a subtle tang. Use the same volume.