How to Make It
Preheat oven to 350°.
Combine first 3 ingredients in a 2-cup glass measure. Microwave at high 2 minutes; let stand 2 minutes. Add butter, stirring until melted. Cool to room temperature.
Lightly spoon flour into dry measuring cups, and level with a knife. Combine flour, 2/3 cup sugar, baking powder, and salt in a large bowl; make a well in center of mixture. Combine milk mixture and egg, and add to flour mixture, stirring just until moist. Spoon batter into 12 muffin cups coated with cooking spray. Sprinkle 1 tablespoon sugar evenly over muffins.
Bake at 350° for 20 minutes or until the muffins spring back when lightly touched in center. Remove the muffins from the pan immediately, and place on a wire rack.
Note: Store the remaining muffins in a heavy-duty zip-top plastic bag in the freezer for up to 2 months. Thaw at room temperature.