Carmelized Onion and Potato Flan

Yesterday I made this potato dish to go with our dinner. It was quick to prepare, easy to do, and quite good. We will have the leftovers today with our meal. It is sort of like Scalloped Potatoes, but a little different. I can't remember where the recipe came from because I had copied it into my own writing, and I just found the recipe in my collection.

Ingredients
2 Tbsp. butter (not oil or margarine)
2 large onions, thinly sliced
6-8 medium potatoes, peeled, washed, and thinly sliced
salt and pepper, to taste
1 cup grated cheese (I used mozzarella)

Directions
In a large frying pan, cook the onions over medium high heat in the butter just until they begin to brown. Reduce the heat to medium low and cook sowly for about 20 minutes, to carmelize and release their juices.

Arrange half of the potato slices shingle-style in the bottom of a greased 9x13 inch metal baking dish. Season, top with half of the onions and half of the cheese. Repeat layers.
Cover with foil, bake at 375◦F for 50-60 minutes until potatoes are tender.