Heat oven to 400ºF. Put cups in 12-muffin cup pan.
Beat milk, butter and egg in a medium bowl.
Add in flour, sugar, baking powder, and salt all at once and stir just until flour is moistened. (Batter will be lumpy; do not over stir.)
Fill muffin cups 3/4 full. Bake until golden brown (16 to 20 minutes).
Immediately remove from pan and carefully roll hot muffin tops in melted butter, then in cinnamon-sugar mixture. Serve warm!