Slow Cooker Caramelized Onion and Gruyère Waffles

Name: Slow Cooker Caramelized Onion and Gruyère Waffles
Prep time: 20 min
Cook time: 45 min
Total time: 1 h 5 min
Yield: 4 servings
Cuisine: French
Ingredients: 4 whole (800 g) yellow onions, large, thinly sliced into half-moons; 3 tablespoons (43 g) unsalted butter, cut into small pieces; ¾ teaspoon (4 g) kosher salt; 2 sprigs (1 g) fresh thyme sprigs (optional); 1¾ cups (220 g) all-purpose flour; 2 teaspoons (10 g) baking powder; ½ teaspoon (3 g) kosher salt; ¼ teaspoon (½ g) freshly ground black pepper; 3 whole (150 g) large eggs, at room temperature; 4 tablespoons (57 g) unsalted butter, melted, cooled slightly; 1¼ cups (300 ml) buttermilk, at room temperature; 1½ cups (150 g) Gruyère cheese, finely grated; 1 teaspoon (5 g) Dijon mustard (optional)

From the MyKitchenBank Kitchen

Crispy-edged waffles studded with sweet, deep caramelized onions and melting Gruyère cheese. The slow cooker does the heavy lifting of caramelizing onions over hours, while the batter comes together quickly for a sophisticated savory brunch or appetizer.

Prep: 20 min
Cook: 45 min
Wait: 8 hr
Total: 9 hr 5 min
Makes: 8 waffles (2 per person)

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Ingredients

4 servings

For the caramelized onions
4 whole (800 g) yellow onions, large, thinly sliced into half-moons
3 tablespoons (43 g) unsalted butter, cut into small pieces
¾ teaspoon (4 g) kosher salt
2 sprigs (1 g) fresh thyme sprigs (optional)
For the waffles
1¾ cups (220 g) all-purpose flour
2 teaspoons (10 g) baking powder
½ teaspoon (3 g) kosher salt
¼ teaspoon (0.5 g) freshly ground black pepper
3 whole (150 g) large eggs, at room temperature
4 tablespoons (57 g) unsalted butter, melted, cooled slightly
1¼ cups (300 ml) buttermilk, at room temperature
1½ cups (150 g) Gruyère cheese, finely grated
1 teaspoon (5 g) Dijon mustard (optional)

Equipment (9)

4-quart slow cooker
Waffle iron
Large mixing bowl
Medium mixing bowl
Whisk
Rubber spatula
Measuring cups and spoons
Sharp knife and cutting board
Box grater or microplane

Steps

Before you start

Prepare onions 8 hours ahead: slice and place in slow cooker with butter and salt to caramelize
Preheat waffle iron for 10 minutes before making waffles
Have all dry ingredients measured out before starting the wet ingredients
Make sure Gruyère is grated just before mixing batter

1
Start slow cooker onions
- Place sliced onions in a 4-quart slow cooker.
- Add the 3 tablespoons (43 g) of butter, 0.75 teaspoon (4 g) salt, and thyme sprigs if using.
- Stir well to coat.
- Cover and cook on low for 8 hours, stirring every 2 hours if possible (or at least once or twice during cooking).
- The onions will turn a deep golden brown and become very soft and sweet.
- If liquid pools at the bottom, drain it off before using in the waffles.
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Ready when: Onions are deep golden brown, very soft, and nearly melted in appearance
Tip: Stirring periodically helps the onions brown evenly and prevents the bottom from burning. Don't skip this step—slow caramelizing produces far sweeter onions than stovetop methods.
2
Cool and measure caramelized onions
- Transfer the caramelized onions to a bowl and let cool for 10 minutes.
- Measure out 1 cup (about 200 g) of the caramelized onions to use in the waffle batter (you may have extra; reserve for serving or other uses).
- Gently chop or break up any large clumps.
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Ready when: Onions are cool enough to handle comfortably and slightly broken up
Tip: Don't skip the cooling step—adding hot onions directly to the batter can partially cook the eggs.
3
Whisk dry ingredients
- In a large mixing bowl, whisk together 1.75 cups (220 g) flour, 2 teaspoons (10 g) baking powder, 0.5 teaspoon (3 g) salt, and 0.25 teaspoon (0.5 g) black pepper until well combined.
- Set aside.
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Ready when: Dry ingredients are evenly mixed with no streaks of baking powder visible
Tip: Whisking distributes the leavening evenly so your waffles rise consistently.
4
Combine wet ingredients
- In a medium mixing bowl, whisk together 3 room-temperature eggs until slightly frothy.
- Add 4 tablespoons (57 g) of cooled melted butter and 1.25 cups (300 ml) buttermilk.
- Whisk until smooth.
- Stir in the 1 teaspoon (5 g) Dijon mustard if using (it adds subtle depth without a spicy kick).
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Ready when: Wet ingredients are smooth and homogeneous with no streaks of egg white
Tip: Room-temperature eggs and buttermilk combine more smoothly and produce a more tender waffle.
5
Combine and fold in mix-ins
- Pour the wet ingredients into the dry ingredients.
- Using a rubber spatula, fold gently until just combined—the batter should still be slightly lumpy with a few streaks of flour visible.
- Fold in the 1.5 cups (150 g) grated Gruyère cheese and the 1 cup (about 200 g) of measured caramelized onions, folding until evenly distributed but taking care not to overmix.
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Ready when: Batter is just combined with some lumps remaining and cheese and onions distributed throughout
Tip: Overmixing develops gluten and makes tough, dense waffles. A few lumps are fine and will disappear as waffles cook.
6
Preheat waffle iron
- Preheat your waffle iron on medium-high heat for about 10 minutes.
- A light mist of cooking spray or a small brush of melted butter on both grids prevents sticking.
- The iron is ready when a few drops of water sizzle and immediately evaporate on contact.
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Ready when: Water droplets sizzle and evaporate immediately on the grids
Tip: A properly preheated iron is key to crispy exteriors. Don't rush this step.
7
Cook first batch of waffles
- Pour about 0.75 cup (180 ml) of batter into the center of the preheated waffle iron.
- Close the lid gently and cook for 4–5 minutes, until the waffle is golden brown and crispy on the outside.
- Most modern waffle irons have a timer or indicator light; if yours doesn't, peek after 4 minutes.
- The waffle should resist slight pressure and release easily from the grids.
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Ready when: Waffle is golden brown and crispy, releases easily from grids, and feels firm when pressed gently
Tip: Don't lift the lid too early or too often—steam escapes and waffles won't be as crispy. Resist the urge to peek before 4 minutes.
8
Transfer and keep warmOven 200°F / 95°C
- Carefully lift the finished waffle from the iron onto a wire rack or oven-safe plate.
- If you'd like to keep them warm and crispy while you finish cooking the remaining three waffles, place them on a sheet pan in a 200°F (93°C) oven—don't stack them, as stacking creates steam and softens the waffles.
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Tip: Using a wire rack instead of a plate allows air to circulate underneath, keeping the bottom crispy as they rest.
9
Cook remaining three waffles
- Repeat step 7 three more times with the remaining batter, cooking each waffle for 4–5 minutes until golden and crispy.
- You should have 8 waffles total (2 per person).
- If the waffle iron seems to be cooking faster or slower, adjust the time slightly for later waffles—every iron is different.
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Ready when: All waffles are golden brown and crispy on the exterior, firm when pressed gently
Tip: The batter will thicken as it sits; if the last waffles seem too thick to pour, thin it with 1–2 tablespoons of buttermilk.
10
Serve warm
- Serve waffles immediately while they're still warm and crispy.
- They're delicious on their own, but optional toppings include a dollop of crème fraîche, extra caramelized onions (from the slow cooker), a fried egg, crispy bacon or pancetta, or a small handful of fresh thyme leaves.
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Tip: Savory waffles are best eaten soon after cooking; they lose their crispness after 30 minutes or so.

Good to know

Tips

The slow cooker does almost all the work here—don't rush the onions. Caramelizing on the stovetop takes 45 minutes of constant attention and won't achieve the same depth. The slow method is truly set-and-forget.
Room-temperature eggs and buttermilk are crucial for a tender crumb. Pull them out of the fridge 30 minutes before mixing.
Grate the Gruyère cheese fresh just before mixing into the batter. Pre-shredded cheese contains anti-caking agents that can create dry spots in your waffles.
These waffles are savory but not spicy. If you like heat, add a pinch of cayenne pepper or smoked paprika to the dry ingredients, or serve with a hot sauce or spicy mayo on the side.

Make ahead

The caramelized onions can be made up to 3 days ahead and stored in an airtight container in the refrigerator. Reheat gently before folding into the batter. The waffle batter (without the onions and cheese, which should be folded in just before cooking) can sit at room temperature for up to 30 minutes, though waffles will be slightly less tender if the batter sits longer.

Storage & reheating

Best eaten fresh and warm. Leftover waffles can be refrigerated in an airtight container for up to 2 days. Reheat in a toaster oven at 350°F (175°C) for 3–4 minutes until crispy again. Waffles can be frozen on a sheet pan for 1 hour, then transferred to a freezer bag and stored for up to 2 months. Toast from frozen in a regular toaster on medium heat for about 4 minutes per side, or warm in a 350°F (175°C) oven for 6–8 minutes.

Substitutions

buttermilk → whole milk mixed with 1 tablespoon lemon juice or white vinegar per 1 cup milk; let sit for 5 minutes before using. Creates a similar tang and rise in the waffles.
Gruyère cheese → aged cheddar or a mix of cheddar and Emmental cheese. Both melt well and provide a sharp, tangy flavor. Avoid pre-shredded cheese, which contains anti-caking agents.
yellow onions, large → a mix of yellow and white onions, or red onions for a slightly fruitier flavor. All three caramelize beautifully. Red onions are sweeter and less sharp.
baking powder → 1.5 teaspoons baking powder plus 0.5 teaspoon baking soda with an extra 1 tablespoon buttermilk or lemon juice. Baking soda adds extra lift and creates a crispier exterior when buttermilk is present.