Heat oven to 375° Lightly grease 13x9-inch baking pan/casserole dish or 2, 14 oz cast iron skillets.
Whisk milk, melted butter and eggs together. Add 2 packages of cornbread mix and stir until combined. Spread half of batter into prepared dish. If using skillets, spoon about 1/4 batter into each skillet.
Layer leftovers evenly on top of batter.
Spoon remaining batter over leftovers and spread evenly.
Bake 55-65 (for 13x9-inch pan) or 18-25 minutes (for skillets) or until cornbread is cooked all the way through (when toothpick inserted into center comes out clean).
Let cool 5 minutes. Serve with warm gravy on the side.