Step 1: Preheat your oven to 375°F (190°C). Grease a 9x13-inch casserole dish.
Step 2: In a large bowl, combine the ground beef, chopped onion, minced garlic, breadcrumbs, milk, egg, Worcestershire sauce, salt, and pepper. Mix until well combined but do not overmix.
Step 3: Transfer the meat mixture into the prepared casserole dish and shape it into a loaf, spreading it evenly across the bottom.
Step 4: Spread the ketchup evenly over the top of the meatloaf layer, ensuring it covers the surface well.
Step 5: In a large pot, bring salted water to a boil and add the sliced potatoes. Cook until tender, about 15-20 minutes.
Step 6: Drain the potatoes and return them to the pot. Add sour cream, milk, butter, salt, and pepper. Mash until smooth and creamy.
Step 7: Spread the mashed potatoes over the meatloaf layer in the casserole dish.
Step 8: Sprinkle the shredded cheddar cheese on top of the mashed potatoes, followed by the chopped green onions.
Step 9: Bake in the preheated oven for 30-35 minutes, or until the cheese is melted and bubbly.
Step 10: Remove from the oven and let it cool for a few minutes before slicing. Serve warm and enjoy your hearty Loaded Potato & Meatloaf Casserole!