Heat the oven to 350º. Place the butter and milk for the batter in a small saucepan over medium heat. Warm the mixture, stirring occasionally, until the butter melts, then transfer the mixture to a small bowl to cool.
Meanwhile, prepare the pine-apple topping. Into each cup of a 12-cup muffin pan, add 1/2 tablespoon of unmelted butter, then evenly sprinkle 1 tablespoon of brown sugar over the bottom. Place the pan in the oven until the butter melts, about 3 minutes.