1. Preheat & Prepare:

1. Preheat oven to 375°F (190°C). Grease a 9×13-inch baking dish.
2. In a large pot, bring salted water to a boil and cook diced potatoes for 5-7 minutes, until just fork-tender. Drain and set aside.

2. Make the Sauce:

1. In a saucepan over medium heat, melt butter. Add onions and garlic, sautéing until soft (about 3 minutes).
2. Stir in the flour and cook for 1-2 minutes, stirring constantly.
3. Gradually whisk in the milk and chicken broth, stirring until thickened.
4. Add salt, pepper, garlic powder, onion powder, and paprika. Remove from heat.
5. Stir in 1 cup of cheddar cheese, mozzarella (if using), and sour cream until smooth.

3. Assemble the Casserole:

1. In a large bowl, combine the cooked potatoes and diced ham. Pour the cheese sauce over the mixture and stir to coat.
2. Transfer to the prepared baking dish and spread evenly.
3. Sprinkle the remaining ½ cup of cheddar cheese on top.

4. Add the Topping & Bake:

1. In a small bowl, mix crushed crackers (or breadcrumbs) with melted butter. Sprinkle over the casserole.
2. Bake uncovered for 25-30 minutes, or until bubbly and golden brown.
3. Let sit for 5 minutes before serving