Boil potato in jackets, cool, peel and slice.

Peel squashes (zucchinis could be used unpeeled), cut into circles.

Put the potato slices and squash circles in a greased baking pan, alternating layers, sprinkle each layer with salt, pepper and grated cheese.

Chop onion and sautee in melted butter. Whisk egg together with milk and onion.

Cover the vegetables with the egg mix, sprinkle with the remaining cheese and bake over 390F for 45 minutes.