Preheat oven to 350°F (175°C). Beat butter and sugar until fluffy, about 2 minutes. Add egg and vanilla, then mix in flour, baking powder, and salt to form a dough.

Shape dough into a disc, wrap in plastic, and refrigerate for at least 30 minutes.

On a floured surface, roll dough to 1/4 inch thick and cut out 2 1/2-inch rounds. Place on lined baking sheets.

Bake 8 to 10 minutes until edges are set and tops are pale. Cool completely on a rack.

Whisk powdered sugar with milk and vanilla to make icing. Divide and color one portion black. Spread white icing on cookies, then pipe or dot black spots. Let set 20 minutes.