Preheat your oven to 350°F (175°C) and lightly grease a 9×13-inch baking dish.
In a skillet, brown the ground beef and diced onion until fully cooked; drain any excess grease.
Stir in condensed cheddar soup, cream of mushroom soup, 1 cup milk, salt, pepper, and 1 cup shredded cheese until smooth and melted.
Spread the beef mixture evenly in the baking dish and sprinkle the remaining cheese on top.
In a bowl, mix Cheddar Bay Biscuit mix, remaining milk, and a handful of cheese until combined. Pour evenly over the beef layer.
Bake uncovered for 50–55 minutes or until golden brown.
Brush the hot biscuit topping with melted butter mixed with the biscuit seasoning before serving.
Let rest for 10 minutes before slicing for best results.
