Mix Your Dough: In a stand mixer, combine flour, baking powder, salt, powdered sugar, and granulated sugar until well blended. Gradually add the softened butter and vanilla extract, mixing until a soft dough ball forms.
Color Your Love: Divide the dough evenly into two portions. Place one half back in the mixer, add the red food coloring, and mix until the dough is uniformly red.
Roll and Chill: Place each dough portion between two sheets of wax paper. Roll them out into approximate 11x9-inch rectangles, about ¼ inch thick. Transfer both dough sheets (still between wax paper) to a baking sheet and chill in the refrigerator for at least 1 hour until firm. This helps with a clean swirl!
Layer Up: Once chilled, remove the top wax paper from both dough sheets. Lightly brush the plain vanilla dough with a touch of water. Carefully flip the red dough sheet on top of the vanilla dough, aligning the edges perfectly. Gently press the edges to seal them together. Trim the sides for a neat rectangle.
Create the Swirl: Starting from a long side, tightly roll the layered dough into a log, like a jelly roll. Keep it snug for a beautiful swirl!
Add Some Sparkle: Pour your Valentine's sprinkles onto a plate. Gently roll the dough log over the sprinkles to coat the outside. Wrap the log tightly in plastic wrap and chill in the refrigerator for a few hours (or freeze for later). This firming step prevents spreading during baking.
Slice and Bake: Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper. Slice the chilled dough log into ¼-inch thick cookies. Place them on the prepared baking sheet.
Golden Perfection: Bake for 10 to 12 minutes, or until the edges are just lightly golden. Let them cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely. Enjoy your homemade, beautiful swirl cookies!