In a bowl, cream together the softened butter and granulated sugar until light and fluffy.

Beat in the egg and vanilla extract until well combined.

In another bowl, whisk together the flour, baking powder, and salt.

Gradually mix the dry ingredients into the wet mixture on low speed until a soft dough forms.

Divide the dough into three equal portions.

Add a few drops of gel food coloring to each portion: one pink, one blue, and one yellow or orange, kneading until colors are well distributed.

Roll each colored dough into rectangles about ¼ inch thick on a floured surface.

Stack the colored rectangles, pressing gently to adhere.

Starting from one long side, tightly roll the layers into a log and seal the edges.

Wrap the log in plastic wrap and refrigerate for at least 2 hours, or overnight.

Preheat your oven to 375°F (190°C) and line baking sheets with parchment paper.

Roll the chilled log in extra granulated sugar to coat.

Slice the log into ¼ inch rounds and place them on the baking sheets.

Bake for 8-10 minutes, until the edges are lightly golden and centers are soft.

Allow to cool on baking sheets for a few minutes before transferring to a wire rack.