Scalloped Potatoes

3 T butter melt cook add add cook until thick and bubbly simmer 8 minutes bake 45 minutes at 375°F
1 onion  
3 T flour  
2 t salt  
¼ pepper
3 c milk  
6 c thinly-sliced potatoes  
  1. In a large saucepan, melt butter over medium-low heat.
  2. Cook onions until tender.
  3. Stir in flour until smooth and bubbly.
  4. Stir in salt and pepper.
  5. Gradually add milk, stirring until thick and bubbly.
  6. Add sliced potatoes to the sauce. Cover and simmer for 8 minutes.
  7. Transfer mixture to a greased 12x8 inch baking dish. Bake, uncovered, at 375°F for 45 minutes, or until potatoes are tender.