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French Onion Frittata
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French Onion Frittata

A delicious frittata featuring caramelized onions and Gruyère cheese, perfect for breakfast or brunch.
Prep Time10 minutes
Cook Time40 minutes
Total Time50 minutes
Servings: 4

Ingredients

Main Ingredients

  • 2 tablespoons unsalted butter divided
  • 2 cups diced day-old bread
  • 1 tablespoon olive oil
  • 2 large yellow onions thinly sliced
  • 1.5 teaspoons kosher salt divided
  • 1 tablespoon balsamic vinegar
  • 8 large eggs
  • 0.25 cup whole or 2% milk
  • 1 tablespoon Dijon mustard
  • 0.25 teaspoon freshly ground black pepper
  • 0.5 cup diced Gruyère cheese (2 ounces)
  • 1 tablespoon finely chopped fresh chives

Instructions

Cooking Instructions

  • Preheat the oven to 400°F and position a rack in the middle.
  • Melt 1 tablespoon of butter in a 10-inch cast iron skillet over medium heat until it bubbles. Add the bread cubes and stir to coat them in the butter, making sure they are in a single layer. Toast the bread for about 5 minutes, turning occasionally, until golden brown all over. Remove the toasted bread and set it aside in a bowl.
  • Lower the heat to low. In the same skillet, add the olive oil, onions, and 1/2 teaspoon of kosher salt. Cook the onions, stirring every 5 to 10 minutes and scraping up any browned bits from the bottom, until they are soft and deeply browned. This will take about 40 minutes. Once they are ready, add the balsamic vinegar and scrape up the browned bits again.
  • In a large bowl, whisk together the eggs, milk, Dijon mustard, the remaining 1 teaspoon salt, and black pepper. Stir the remaining butter and croutons back into the skillet, spreading them evenly. Pour the egg mixture over the ingredients in the skillet and tilt the pan to help the eggs distribute evenly. Top with Gruyère cheese. Cook on the stovetop until the edges begin to set, which should take about 2 to 4 minutes.
  • Transfer the skillet to the oven and bake until the eggs are fully set, taking about 8 to 10 minutes. To check for doneness, cut a small slit in the center; if raw egg runs out, continue baking for a few more minutes. Once set, remove from the oven.
  • Allow it to cool in the pan for 5 minutes. Before serving, sprinkle with chives, then slice into wedges and serve warm.

Notes

You can prepare the croutons up to a week beforehand and keep them in an airtight container at room temperature. The caramelized onions can be made up to 3 days in advance and should be stored in an airtight container in the refrigerator, or they can be frozen for up to 3 months. Any leftovers should be kept in a covered container in the refrigerator for up to 5 days.