Cream together 1 cup unsalted butter and 1 cup powdered sugar until light and fluffy (about 3 minutes). Add 2 eggs and 2 tbsp milk, mixing well.

Divide dough into three equal parts. Leave one white, color second with purple gel, and last with black gel.

Roll black and white dough into 6x12-inch rectangles. Stack with white on top of black and roll together to seal layers.

Roll purple dough into 6-inch wide rectangle, sprinkle purple sprinkles, and roll into a log.

Place purple log at end of black-and-white layers and roll to enclose purple log.

Roll dough log in black or chocolate sprinkles, wrap in plastic wrap, and chill for at least 1 hour.

Preheat oven to 375°F (190°C). Slice chilled log into ¼-inch rounds and place on lined baking sheets.

Bake for about 10 minutes until edges are set. Cool on pan for 10 minutes before transferring to a wire rack.