Preheat the oven to 350°F (175°C) and prepare a baking sheet lined with parchment paper.

In a medium bowl, whisk together all-purpose flour, baking powder, baking soda, and salt until well combined.

Beat together softened unsalted butter and granulated sugar in a large mixing bowl for 2-3 minutes until fluffy.

Add large egg, vanilla extract, and buttermilk to the butter and sugar mixture, mixing on low until combined.

Gradually add dry ingredients to the wet mixture, mixing until just combined to form a slightly sticky dough.

Divide the dough into two equal parts, coloring one half with pink and the other with blue gel food coloring.

Roll small amounts of pink and blue dough into balls and gently swirl them together before placing on the baking sheet.

Bake for 10-12 minutes until edges are lightly golden while centers remain soft.

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