Brown the meat: Heat a large non-stick skillet over medium-high heat. Add the lean ground beef and diced yellow onion, cooking for 7-10 minutes until browned.

Mix in the soups: Reduce heat to medium and stir in the condensed cheddar soup and cream of mushroom soup with milk, salt, and pepper. Heat for 3-5 minutes.

Add the cheese: Stir in the shredded cheddar cheese until melted, then transfer to a greased 9x13-inch baking dish.

Prepare the biscuit topping: Combine Cheddar Bay biscuit mix, remaining cheese, and additional milk in a bowl. Dollop over the beef filling.

Bake to perfection: Preheat oven to 350°F (175°C) and bake for 50-55 minutes until the topping is golden brown.

Finish with butter: Brush melted butter over the biscuit topping before serving. Rest for 5 minutes.