01 - Set oven to 375°F (190°C) to preheat while preparing other ingredients.
02 - In a skillet over medium-high heat, brown ground beef with diced onion until meat is cooked through; drain excess fat.
03 - In a large bowl, combine condensed cream of mushroom soup, whole milk, and garlic powder. Mix until smooth.
04 - Grease a 9x13 inch (23x33 cm) baking dish. Spread the cooked beef and onion mixture evenly on the bottom, followed by the soup mixture. Distribute frozen tater tots in an even layer on top.
05 - Place dish in oven and bake for 35 minutes, or until tater tots are crisp and golden.
06 - Sprinkle shredded cheddar cheese evenly over casserole and bake for an additional 10 minutes, or until cheese is melted and bubbling.
07 - Remove from oven and let casserole rest 5 minutes before serving. Season with salt and black pepper as desired.