Preheat oven to 375° F. In a large bowl beat butter with an electric mixer on medium to high speed for 30 seconds. Add granulated sugar, brown sugar, baking powder, and salt. Beat until mixture is combined, scraping sides of bowl occasionally. Beat in egg, milk, and vanilla until combined. Beat in as much of the flour as you can with the mixer. Stir in any remaining flour.
Shape dough into 3/4-inch balls. For each full snowman cookie, on an ungreased or parchment paper-lined cookie sheet, place 2 dough balls side by side with one side touching. Press thumbs into each ball to form an indentation in each. Repeat with remaining dough balls, leaving about 2 inches between cookies. For heads only, use one dough ball.
Bake for 7 to 9 minutes or until edges are lightly browned. Remove from oven and transfer cookies to a wire rack. Let cookies cool. Fill each indentation with the icing (I used decorating bags and #2 or #3 tip. Let icing dry for several hours.
Tint some of the royal icing black, and some orange. Using a small decorating (#1) tip and black icing, apply buttons and eyes. With the orange, add a carrot nose.
Let cookies dry completely, ENJOY!