French onion soup enhances frittata
This is the frittata to keep handy when you need a breakfast that impresses. A mash-up of frittata and French onion soup, it is pure comfort food.
The eggs are loaded with rich, velvety caramelized onions and gooey, melted Gruyere. Cubes of toasted bread are even studded throughout the eggs.
When you add the sliced onions to the skillet, it might seem as if this recipe calls for too many. The thing about caramelizing onions is they cook down a lot, which concentrates their flavor.
Because it takes a while to caramelize onions, I make them ahead of time. middle of the oven and heat to 400 degrees.
Heat 1 tablespoon of the butter in a 10-inch cast-iron skillet over medium heat until bubbling. Add the bread and toss to coat. Toast, tossing every minute or so, until the cubes are golden-brown, about 5 minutes. Transfer to a bowl; set aside.
Reduce heat to low. Add oil, onions and ½ teaspoon of salt to the skillet. Cook until the onions are soft and browned, about 40 minutes. Add vinegar and scrape up bits from pan.
Whisk together eggs, milk, mustard, 1 teaspoon salt, and pepper in a bowl. Stir 1 tablespoon butter and croutons into the skillet; spread in an even layer. Pour the egg mix on and tilt the pan to ensure eggs settle evenly. Top with cheese. Cook 2 to 4 minutes, then bake until eggs are set, 8 to 10 minutes.
To check, cut a slit in the center. If raw eggs run into the cut, bake for another few minutes.
Cool in the pan for 5 minutes and top with chives. Slice into wedges and serve warm.