Creamy Scalloped Potatoes

Ingredients

2 lb potatoes (about 6 medium)
1/4 tsp pepper
3 tbs butter
1 small onion, thinly sliced
1 can cream of mushroom soup
1/4 c flour
1 tsp salt
4 slices American cheese

Directions

Peel 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, or 3 to 4 hours on high. Add cheese slices 30 minutes before serving.