In a large bowl, combine the ground beef, chopped onion, minced garlic, breadcrumbs, milk, egg, Worcestershire sauce, salt, and black pepper. Mix well.
Press the meatloaf mixture into the bottom of a greased 9x13-inch baking dish.
Spread the ketchup evenly over the top of the meatloaf.
In a separate bowl, combine the sliced potatoes, sour cream, milk, butter, shredded cheddar cheese, and chopped green onions. Season with salt and pepper to taste.
Spread the potato mixture evenly over the meatloaf layer.
Bake in the preheated oven for 60 minutes, or until the meatloaf is cooked through and the potatoes are tender.
Let the casserole rest for 5 minutes before serving.
Notes
You can add additional toppings like bacon bits or extra cheese before baking if desired.