In a skillet, cook 1 lb ground beef with 1 small diced onion over medium-high heat until browned. Drain grease.
Stir in 1 tsp minced garlic and cook for 1 minute.
Add 1 cup corn, 1 (10.5 oz) can cream of mushroom soup, ½ cup shredded cheddar cheese, ½ cup milk, ¼ cup sour cream, 1 tsp salt, and ½ tsp black pepper. Stir to combine.
Pour mixture into a 9×13 baking dish.
Top with 1 (32 oz) bag tater tots in a single layer.
Bake for 20–25 minutes until tots are cooked.
Top with remaining ½ cup cheddar cheese and bake 5 more minutes until melted.