Oven 375 deg F
Brush 9" square baking dish with oil.
Bring water to a simmer in a large skillet. Add leeks garlic and potatoes: season with 1/2 teaspoon salt. Cook covered until potatoes are just tender, 8 to 10 minutes. Let cool.
Whisk together eggs, whites, 1/2 teaspoon salt and the cayenne. Fold in the potato mix and ricotta. Mix in 1/4 cup of the parmesan. Pour into dish and sprinkle remaining parmesan. Bake until edges are set, about 12 minutes. Reduce oven temp to 325 deg F, and bake until knife inserted in center comes out clean, 20 to 25 minutes. Let cool for 10 minutes. Cut into 8 squares.