Boil potatoes 20 minutes. Drain.

Preheat oven to 350

Grease baking dish

Melt 3 tbs butter in pot over medium heat, add onion, cook until tender, add ham and potatoes then place in dish

Melt 1/4 cup of butter in pot, add flour, add salt & pepper, gradually whisk in milk until thick, reduce heat, add cheddar cheese, pour sauce over the mixture in the dish, sprinkle bread crumbs on top

Cover with foil and cook 25-30 minutes