Ham and Potato Casserole Recipe

Ingredients
2 tablespoons unsalted butter (¼ stick)
1 yellow onion finely diced
3 tablespoons all-purpose flour
1¼ cups whole milk or half-and-half
½ cup chicken stock or chicken broth
½ teaspoon fine sea salt
½ teaspoon ground black pepper
½ teaspoon garlic powder
2 pounds russet potatoes peeled and diced small
2½ cups diced cooked ham
4 ounces freshly shredded white cheddar cheese (about 1 cup)
Instructions