Prepare the Potato Crust
Begin by tossing the sliced potatoes in melted butter and salt. Arrange the potato slices evenly on the bottom and up the sides of a greased 13x9-inch baking dish. Bake in a preheated oven at 400°F for 25-30 minutes, or until the potatoes are nearly tender.
Cook the Ground Beef and Prepare the Filling
While the potatoes bake, heat a large skillet over medium heat and cook the ground beef until browned, ensuring it is fully cooked through. Drain any excess fat. Spread the beef evenly over the baked potatoes, followed by the frozen corn. In a separate bowl, combine the cream of celery soup, milk, garlic powder, pepper, onion, and half of the shredded cheddar cheese. Pour this mixture over the beef and corn layers.
Final Baking and Topping
Return the casserole to the oven and bake uncovered at 400°F for an additional 20 minutes, or until the vegetables are tender. Sprinkle the remaining cheese over the top and bake for another 2-3 minutes, or until the cheese has fully melted. Optionally, garnish with minced parsley before serving.