Au Gratin Potatoes

6 medium potatoes

¼ cup margarine or butter

1 medium onion, chopped

1 Tbsp. flour

1 tsp. salt

½ tsp. pepper

2 cups milk

2 cups cheddar cheese, shredded

½ cup bread crumbs

Preheat oven to 375 degrees.  Cut potatoes into 1/8 inch slices, enough to measure 4 cups worth.  In saucepan over medium heat melt margarine.  Cook onion in margarine about 2 minutes, stir constantly, until tender.  Stir in flour, salt and pepper.  Cook and stir until bubbly.  Remove from heat.  Stir in milk and 1 ½ cups cheese.  Heat to boiling, stir constantly.  Boil and stir 1 minute.  Spread potatoes in ungreased 1 ½ casserole dish.  Pour cheese sauce over potatoes.  Bake uncovered 1 hour.  Mix remaining cheese and bread crumbs, sprinkle over potatoes.  Bake 15-20 minutes longer until top is brown and bubbly.