Ham and Potatoes "2" (Large Casserole)

4 large russet potatoes, peeled, diced large, and cooked until just tender - do not overcook
3 - 4 cups leftover ham, diced
1 large onion, diced

For Sauce:
2 TBS butter
2 TBS flour
1 tsp salt
1/4 tsp pepper
2 cups milk
1 can cream of chicken soup - undiluted
2 cups shredded cheddar cheese

In a medium saucepan, melt butter; stir in flour and cook together about 2 minutes to form a roux.
Add salt and pepper.
Stir in milk and cook & stir until mixture thickens.
Add soup and cook until smooth.
Add cheese and stir until melted.

In a large mixing bowl, toss together potatoes, ham, and onions.
Pour sauce over all and mix until well combined.
Bake at 350 about 45 minutes or until hot and bubbly.