Creamy Crock-Pot Potatoes

Toss potato slices in 1 cup water and 1/2 teaspoon cream of tartar. Drain and put half of potatoes in greased crock-pot. Top with half of onion, flour, salt and pepper.

Layer with potatoes and onion, salt, pepper and flour again. Pour soup and butter on top. Cover and cook on low 7 to 9 hours or on high 2 to 4 hours. Add 4 slices American cheese to top 30 minutes before serving.