2 medium yellow squash, cut into 1/4 inch rounds (2.5 cups)
1 packed tablespoon thinly sliced fresh sage or basil leaves
10 large eggs
1/4 cup water
1/2 teaspoon salt
1/4 cup coarsely shredded Gruyère cheese
Grease a 12inch non-stick ovenproof skillet over medium-high heat. Add squash and saute 8 minutes; stir in sage. Cook just 1 to 2 minutes more until tender and browned in spots.
Arrange oven rack 6 inches from heat source, heat broiler. Wisk eggs, water and salt in a bowl. Melt 1 tblspoon butter in the skilled and pour the eggs over the squash. Reduce heat to medium low, cover and cook until set on bottom and edges, but the top is still loose, about 3 minutes. Sprinkle Gruyere evenly over the top.
Broil frittata until just set, about 1 minute. Cut into wedges to serve.