Preheat the oven to 350°F (175°C).
Cook ground beef and diced onion in a large skillet over medium heat until browned and tender. Drain excess grease.
Add garlic, condensed cheddar soup, cream of mushroom soup, milk, salt, and pepper. Stir until smooth, then mix in 1 cup of shredded cheddar cheese until melted.
Spread the beef mixture evenly into a greased 9×13-inch baking dish. Sprinkle the remaining cheddar cheese over the top.
In a bowl, mix Cheddar Bay Biscuit mix, shredded cheddar cheese, and milk until combined.
Spread the biscuit batter evenly over the casserole. Bake for 50–55 minutes, or until golden and fully cooked.
Mix melted butter with the seasoning packet and brush over the hot biscuits. Let rest for 5 minutes, garnish with parsley, and serve.