1 bunch Swiss chard, tough white stems discarded 2 Tbsp. unsalted butter
1 medium leek (or onion), white and tender green parts thinly sliced 1 tsp. salt, plus more to taste
6 large eggs 4 oz. Gruyere cheese, grated (about ¾ cup)
Freshly ground black pepper to taste
Preheat oven to 425 degrees F. Wash chard in cold water several times. Drain and transfer to a pot. Cover and cook over high heat for 1 to 2 min. or until wilted and bright green. Drain and run under cold water until chilled. Squeeze dry and chop. Heat butter in heavy saute pan. Add leek and 1 tsp. of salt. Cook 5 to 7 min. until softened; regulate the heat to prevent browning. Remove from heat. Crack the eggs into a mixing bowl and whisk briefly. Add the chard, leek, and cheese. Season with plenty of black pepper and, if desired, additional salt. Butter a 9-inch pie plate or cast-iron skillet. Pour in egg mixture and smooth the surface with a spatula. Bake for 35 to 40 min. or until puffed and golden brown. An inserted knife will come out clean when the frittata is ready. Serves 6.