- 4
Ingredients
- 8 large eggs
- Kosher salt and ground black pepper
- 4 tablespoons salted butter, cut into 4 pieces, divided
- 1 medium yellow onion, chopped (about 1 cup)
- 1 medium garlic clove, grated
- 1/4 cup plus 1 teaspoon sherry vinegar
- 1/2 cup grated Parmesan cheese
- 1 tablespoon whole-grain mustard
- 4 tablespoons minced fresh chives, divided
Preparation
Step 1
Heat the oven to 325°F with a rack in the upper-middle position. In a large bowl, beat the eggs with ¾ teaspoon salt and ½ teaspoon pepper.
In a 10-inch ovenproof nonstick skillet over medium-low, melt 1 tablespoon of the butter. Add the onion and ½ teaspoon salt, cover and cook, stirring occasionally, until softened and moisture is released, about 5 minutes. Uncover, increase the heat to medium-high and cook, stirring occasionally, until well browned, about 10 minutes. Stir in the garlic and 1 teaspoon of sherry vinegar. Cook until the vinegar has evaporated, 30 to 60 seconds
Pour the eggs into the skillet and cook, using a silicone spatula to push and stir from the edges to the center, until the eggs begin to set, about 1 minute. Transfer the skillet to the oven and bake until just set, 3 to 5 minutes. Remove from the oven and sprinkle with the Parmesan. Return to the oven and bake until the cheese melts, about 1 minute.
Remove from the oven. Run the spatula around the edge and under the frittata to loosen, then slide onto a serving plate. Sprinkle with 2 tablespoons of the chives. Set the empty skillet over medium-high, add the remaining ¼ cup vinegar and simmer until reduced to 2 tablespoons, 2 to 4 minutes. Off heat, stir in the mustard, then stir in the remaining 3 tablespoons butter a piece at a time until melted. Stir in the remaining 2 tablespoons chives, then taste and season with salt and pepper. Cut the frittata into wedges and serve with the sauce on the side.
Tip: Don't omit the cheese. It adds a savory element that balances the sweetness of the onions. Also, don't use a conventional skillet. Nonstick is essential so that the frittata slides out of the pan with ease.