- 4 tablespoons butter
- 1 large onion, diced
- 4 cups chopped mustard greens (stems discarded and leaves coarsely chopped)
- 8 eggs, beaten
- 1/4 cup heavy cream
- Kosher salt and freshly ground pepper
- 1 cup grated Parmigiano-Reggiano
Preheat the oven to 350°.
- In a large ovenproof skillet, heat 3 tablespoons of the butter. Add the onion and cook over medium heat until translucent.
- Add the mustard greens and cook until wilted.
- Season the eggs with salt and pepper, whisk in the remaining tablespoon of butter and the cream.
- Pour the eggs into the skillet, tilt the pan so it the eggs are evenly distributed and cook over moderate heat for about 10 minutes.
- At this point the bottom and sides should be setting but the top should still be runny.. Sprinkle the Parmigiano-Reggiano on top.
- Transfer the skillet to the oven and bake for about 10 minutes, until the center of the frittata is set and slightly browned. Slide the frittata onto a cutting board.
- Cut into 1 1/2-inch squares and serve hot, warm or at room temperature. Also great as leftovers, reheated and served on a slice of toast.