Preheat oven to 350°F (175°C).
In a large skillet over medium-high heat, cook the ground beef until browned. Drain excess grease.
Add diced onion and minced garlic to the beef and cook until softened, about 3–4 minutes.
Stir in cream of mushroom soup, sour cream, and milk. Season with salt and pepper.
Spread the beef mixture evenly in a 9x13-inch baking dish.
Sprinkle 1 cup of shredded cheddar cheese over the beef mixture.
Arrange frozen tater tots in a single layer over the cheese.
Bake uncovered for 35–40 minutes, until tater tots are golden and crispy.
Sprinkle remaining cheddar cheese on top and bake for another 5 minutes, until melted.
Garnish with chopped parsley before serving, if desired.