Scalloped Potato and Ham Casserole

6 med potatoes
1-1/2 c diced ham
2 tsp margarine (Smart Balance)
1 small onion, finely chopped (about 1/4 c)
3 Tbsp flour
1 tsp salt
1/4 tsp pepper
2-1/2 c 1% milk

Heat 3 Tbsp butter in a 2 qt sauce pan over medium heat. Cook onion in butter about 2 minutes, stirring occasionally. Stir in flour, salt, pepper. Cook, stirring constantly, until smooth and bubbly; remove from heat. Stir in milk. Heat to boiling, stirring constantly. Boil and stir 1 minute.

To Freeze: Freeze sauce in a ziploc baggie and freeze ham in a ziploc baggie, separately.

To Reheat: Grease a 2 qt casserole dish. Slice 6 medium potatoes (about 4 cups). Place a layer of potatoes in the dish, then ham. Continue to layer until dish is full, ending with potatoes on the top. Melt the sauce in a covered sauce pan stirring often, just until melted. Pour over potato casserole. Dot with 1 Tbsp margarine or butter. Cover and bake for 30 minutes. Uncover and bake another 60-70 minutes or until potatoes are tender. Let stand 5 - 10 minutes before serving.