Preheat oven to 425 degrees. Pour melted butter on baking sheet and use a pastry brush to spread all over pan; set aside.
In a large bowl, whisk together the pancake mix, milk, and eggs until well combined. Pour the batter on to the prepared pan and spread evenly using a spatula. Add toppings to the batter and place in preheated oven on center rack.
Bake for 12-15 minutes or until the pancakes are golden brown. Remove from oven and cut into squares. Serve with maple syrup.