2 lbs. potatoes (about 6 med.)
1 sm. onion, thinly sliced
1/4 c. flour
1 tsp. salt
1/2 tsp. pepper
2 tbsp. butter
1 (10 1/2 oz.) can cream of mushroom soup
4 slices American cheese

Pare and thinly slice potatoes. Toss slices in 1 cup water and 1/2 teaspoon cream of tartar. Drain. Put half of sliced potatoes in greased crock pot. Top with half of onion slices, flour, salt, and pepper. Add remaining sliced potatoes and onions. Sprinkle with remaining flour. Add butter and undiluted soup. Cover and cook on low 7 to 9 hours (high 3 to 4 hours). Add cheese 30 minutes before serving. Double recipe for 5 quart model.

I found out that if you cook potatoes in saucepan of water for 10 minutes, then it will cook through good while in the crock pot.