Peel and thinly slice potatoes. Peel, seed, and thinly slice squash.
Cook potato in boiling water to cover in a Dutch oven 5 minutes. Add squash; cover and cook 3 more minutes. Remove from heat, and drain well.
Melt butter in a large skillet; add onion, and saute 10 to 12 minutes or until golden brown.
Layer half of potato slices and squash in a lightly greased 13- x 9-inch baking dish; sprinkle with half of salt and pepper. Top with half of onion, cheese, and Cream Sauce. Repeat layers, ending with Cream Sauce.