Caramelized Onion Frittata

Elevate your breakfast, brunch, or light dinner with this irresistible Caramelized Onion Frittata—a dish that’s as elegant as it is comforting. Made with slow-cooked golden onions sautéed to perfection in a blend of olive oil and butter, this oven-baked frittata is infused with savory Parmesan cheese, a hint of fresh thyme, and a fluffy egg mixture. The result is a rich and flavorful casserole-style dish with a creamy center and subtly sweet, caramelized notes. Ready in under an hour and served straight from a cast iron skillet, this frittata is ideal for entertaining or meal prep, as it can be enjoyed warm or at room temperature. Whether you're looking for a protein-packed start to your day or a quick weeknight dinner, this recipe is a satisfying and wholesome choice.

Nutriscore Rating: 62/100

Prep Time:15 mins

Cook Time:40 mins

Total Time:55 mins

Servings: 4

Ingredients

• 2 tablespoons Olive oil
• 1 tablespoon Unsalted butter
• 2 large Yellow onions
• 0.5 teaspoons Salt
• 0.25 teaspoons Ground black pepper
• 8 pieces Large eggs
• 0.25 cups Whole milk
• 0.5 cups Parmesan cheese (grated)
• 1 teaspoon Fresh thyme leaves (optional)

Directions

Step 1

Peel and thinly slice the yellow onions.

Step 2

In a large oven-safe skillet (preferably cast iron), heat the olive oil and butter over medium heat until melted and shimmering.

Step 3

Add the sliced onions to the skillet and sprinkle with 1/4 teaspoon of salt. Stir to coat the onions in the oil and butter mixture.

Step 4

Reduce the heat to low and cook the onions, stirring occasionally, for 25-30 minutes until caramelized and golden brown. If the onions begin to stick or brown too quickly, add a splash of water and continue cooking.

Step 5

While the onions are caramelizing, preheat your oven to 375°F (190°C).

Step 6

In a medium mixing bowl, whisk together the eggs, whole milk, remaining 1/4 teaspoon of salt, ground black pepper, Parmesan cheese, and fresh thyme if using. Set aside.

Step 7

Once the onions are fully caramelized, spread them evenly across the skillet.

Step 8

Pour the egg mixture over the onions, tilting the skillet gently to ensure the eggs spread evenly. Avoid stirring at this stage.

Step 9

Cook the frittata on the stovetop over medium-low heat for 5-7 minutes, just until the edges begin to set. The center will still be slightly runny.

Step 10

Transfer the skillet to the preheated oven and bake for 10-12 minutes, or until the frittata is puffed and the center is set.

Step 11

Remove the skillet from the oven and let the frittata cool for 5 minutes before slicing.

Step 12

Serve warm or at room temperature, and enjoy!

Nutrition Facts

Serving size	(926.1g)

Amount per serving	% Daily Value*
Calories	1573.2

Total Fat 115.6g	0%
Saturated Fat 46.0g	0%
Polyunsaturated Fat 2.7g
Cholesterol 1621.6mg	0%
Sodium 3586.5mg	0%
Total Carbohydrate 44.4g	0%
Dietary Fiber 5.4g	0%
Total Sugars 15.8g
Protein 98.7g	0%

Vitamin D 346.8IU	0%
Calcium 1677.6mg	0%
Iron 8.9mg	0%
Potassium 1212.7mg	0%

*The % Daily Value tells you how much a nutrient in a serving of food contributes to a daily diet. 2,000 calories a day is used for general nutrition advice.

Source of Calories

Fat: 64.5%

Protein: 24.5%

Carbs: 11.0%