In a medium bowl, whisk together the flour, baking powder, and salt. Set aside.

In a large mixing bowl, beat the butter until smooth. Add the sugar and continue mixing until light and fluffy, about 2 minutes.

Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.

Slowly add the dry ingredients to the wet ingredients in three additions, mixing just until combined.

Divide the dough evenly into three portions. Leave one portion plain, color one red, and color the other blue using gel food coloring.

Shape each dough portion into a flat rectangle and wrap tightly in plastic wrap. Refrigerate for at least 30 minutes until firm but still easy to roll.

On a lightly floured surface, roll each dough portion into rectangles of similar size. Stack the red layer on top of the white layer, then place the blue layer on top.

Gently press the layers together. Starting from the short side, tightly roll the dough into a log. Wrap and refrigerate for at least 2 hours or overnight.

Preheat the oven to 375°F and line baking sheets with parchment paper.

Slice the chilled dough log into ¼-inch thick rounds. Roll the edges in coarse sugar or sprinkles if desired, then place the cookies on the prepared baking sheets.

Bake for 8 to 10 minutes, until the edges are set and the centers remain soft.

Let the cookies cool on the baking sheet for a few minutes before transferring to a wire rack to cool completely.