Preheat your oven to 375°F (190°C) and generously grease a 9×13-inch baking dish. This temperature provides the ideal balance for cooking the meatloaf through while preventing the potato topping from over-browning.
Step 2: Build the Perfect Meatloaf Base
In a large mixing bowl, gently combine ground beef, diced onion, minced garlic, breadcrumbs, milk, egg, Worcestershire sauce, salt, and pepper. Mix with clean hands just until ingredients are evenly distributed – overmixing creates tough, dense meatloaf.
Step 3: Shape and Glaze
Press the meat mixture evenly into your prepared baking dish, creating a uniform layer that will cook consistently. Spread the ketchup evenly over the surface, creating a protective glaze that caramelizes beautifully during baking.
Step 4: Begin the First Bake
Place the dish in your preheated oven for 25 minutes. This initial cooking phase allows the meatloaf to set while you prepare the potato topping.
Step 5: Perfect the Potato Layer
While the meatloaf bakes, bring a large pot of salted water to boil. Add sliced potatoes and cook for 15 minutes until fork-tender. Drain thoroughly and mash with sour cream, warm milk, and melted butter until creamy and smooth.
Step 6: Assemble the Masterpiece
Remove the partially cooked meatloaf from the oven. Carefully spread the seasoned mashed potatoes over the entire surface, creating gentle peaks for extra texture. Sprinkle generously with sharp cheddar cheese and fresh green onions.
Step 7: Complete the Transformation
Return the assembled casserole to the oven for an additional 20 minutes, until the cheese is melted, bubbly, and lightly golden. The internal temperature should reach 160°F for food safety.
