Leek and Spring Onion Frittata

Preheat oven to 350°F. Rinse leek halves under cold water, separating layers and rubbing leaves to remove any grit trapped between layers. Pat dry thoroughly. Cut each leek half crosswise into 2- to 3-inch pieces. Heat oil in a 10-inch nonstick ovenproof skillet over medium. Add leek pieces, cut side down, and spring onion; cook, covered, until bottoms are deeply browned and leek pieces are tender, 8 to 10 minutes. Remove from heat. Carefully remove mixture from skillet, taking care to keep leek pieces intact, and transfer to a plate.

While leek mixture cooks, whisk together eggs, milk, fresh herbs, salt, and pepper in a medium bowl.

Pour egg mixture into skillet; cook over medium, gently stirring often, until eggs form large curds, about 1 minute. Remove from heat. Arrange leek mixture, browned sides facing up, on top of egg mixture in skillet. Sprinkle evenly with cheese. Transfer skillet to oven and bake until center is just set, 10 to 12 minutes. Run a rubber spatula around edge of frittata to loosen from skillet; slide frittata onto a plate. Cut into 4 pieces, and serve.