Amish Stovetop Potatoes Au Gratin

4 Tbsp. butter
3 large potatoes, sliced thin
1 large onion, chopped
1 1/2 cups shredded cheese
2 tsp. salt
Pepper to taste
1/2 cup milk or cream

Melt butter in a 9-inch skillet. Layer potatoes, onions, salt and pepper. Pour milk over it and sprinkle with cheese. Begin cooking on medium heat until cover is very hot. Reduce to low and cook 25 minutes. For the last five minutes, set lid ajar to allow some steam to evaporate.