Cream the butter and sugar with standing mixer or electric beaters, about 1 minute.
Add egg, milk, and vanilla. Beat again for about 30 seconds.
Add flour and baking powder. Beat until JUST incorporated, about 10 seconds.
Roll dough into 1.5″ balls.
SKIP TO THE REINDEER PART, OR KEEP GOING FOR PLAIN COOKIES
Put cinnamon sugar in a tiny bowl to cut down on messes. Dip each ball into the cinnamon sugar and roll around until it’s coated. Place on a baking sheet lined with parchment paper.