Line baking sheets with parchment paper and set aside.
In a large bowl, cream butter and sugar until light and fluffy.
Beat in the egg and vanilla extract until fully combined.
In a separate bowl, whisk together flour, baking powder, and salt.
Gradually mix dry ingredients into wet ingredients until a soft dough forms.
Divide dough evenly into two portions. Leave one plain.
Add pink food coloring to the second portion, mixing until evenly colored.
Roll each dough portion between parchment paper into rectangles about ¼-inch thick.
Place the pink dough on top of the plain dough and gently press together.
Starting from the long edge, roll tightly into a log to form the swirl.
Wrap in plastic wrap and refrigerate for at least 1 hour, until firm.
Preheat oven to 350°F (175°C).
Slice dough into ¼-inch thick rounds and place on prepared baking sheets.
Bake for 10–12 minutes, until edges are set but not browned.
Cool on baking sheet for 5 minutes, then transfer to a wire rack to cool completely.