French Onion Frittata

Ingredients:

• 2 tablespoons unsalted butter, divided
• 2 cups day-old bread, diced
• 1 tablespoon olive oil
• 2 large yellow onions, thinly sliced
• 1 1/2 teaspoons kosher salt, divided
• 1 tablespoon balsamic vinegar
• 8 large eggs
• 1/4 cup whole milk
• 1 tablespoon Dijon mustard
• 1/4 teaspoon freshly ground black pepper
• 1/2 cup Gruyère cheese, diced

Directions:

1. Arrange a rack in the middle of the oven. Heat to 400°F.
2. Heat 1 tablespoon of butter in a 10-inch cast-iron skillet over medium heat until bubbling. Add the bread cubes to the pan, toss to coat with butter, and arrange in a single layer. Toast the bread, tossing every minute or so, repeating until cubes are golden-brown on all sides, about 5 minutes total. Transfer the croutons to a bowl; set aside.
3. Reduce heat to low. Add oil, onions and 1/2 teaspoon of the salt to the skillet. Cook, stirring every 5-10 minutes until the onions are soft and deeply browned, about 40 minutes total. Add vinegar and scrape up the browned bits at the bottom of the pan.
4. Whisk together the eggs, milk, mustard, remaining 1 teaspoon salt and pepper in a large bowl. Stir the remaining butter and croutons into the skillet, then spread in an even layer. Pour the egg mixture over the croutons and tilt the pan so the eggs settle evenly. Top with the cheese. Cook until the eggs at the edges of the skillet begin to set, approximately 4 minutes.
5. Bake in the preheated oven until the eggs are set, 8 to 10 minutes.
6. Cool for 5 minutes. Slice into wedges and serve warm.

Yield: 4-6

Prep time: 30 min

Cook time: 1 hour ten min