DIRECTIONS. STIR in flour and pepper. ADD milk and bring to a boil, stirring constantly. When the potatoes are just fork-tender, you’ll stir in the package of diced ham and finish the top of the casserole with buttered cracker crumbs. Place the dish back in the oven for about 5-7 more minutes – just so that the delicious topping can turn golden brown – and your Cheesy Ham and Potato Casserole is done! The recipe is simple, takes very little time to prepare and cook, and is an excellent way to use leftover ham. HEAT oven to 350 degrees. Roasted potatoes with ham, onion, and seasonings make a fabulous one-dish, everyday meal. COOK onion and green pepper in margarine until tender.