In a medium bowl, whisk together the flour, baking powder, and salt. Set it aside.
In a stand mixer fitted with the paddle attachment (or using a hand mixer), beat the butter on medium speed until smooth and creamy.
Gradually add the sugar and continue mixing until light and fluffy about 2 minutes. Don’t rush this step. Creaming properly gives you that soft texture.
Add the eggs one at a time, mixing well after each addition.
Stir in the vanilla extract.
With the mixer on low speed, add the dry ingredients in three additions. Mix just until combined don’t overmix.The dough should be soft but not sticky. If it feels too soft to handle, that’s okay. Divide the dough evenly into three bowls. Leave one portion plain this will be your white layer. Add red gel food coloring to one portion. Add blue gel food coloring to the other portion.Use gel coloring instead of liquid. It gives you vibrant color without changing the dough’s consistency. Gently knead each colored portion until the color is evenly distributed. If your kids are helping, this is their favorite part just remind them not to overwork the dough.
Shape each portion into a flat rectangle. Wrap tightly in plastic wrap. Refrigerate for at least 30 minutes.You want the dough firm but still pliable. Too soft and it will squish. Too cold and it will crack. On a lightly floured surface, roll each dough portion into a rectangle of similar size and thickness.
Stack the red layer on top of the white layer. Place the blue layer on top. Press gently so the layers adhere don’t press so hard that the colors blend.
Starting from a short edge, roll the dough tightly into a log. Take your time here. Slow and steady gives you clean swirls.
Once rolled: Wrap the log tightly in plastic wrap. Refrigerate for at least 2 hours (or overnight).This long chill is what keeps the cookies from spreading and keeps those colors crisp. Preheat your oven to 375°F (190°C).
Line baking sheets with parchment paper.
Slice the chilled log into ¼-inch thick rounds. If the log flattens slightly while slicing, gently reshape it with your fingers.
Optional: Roll the edges in coarse sugar or sprinkles for a little sparkle.
Place the cookies on your baking sheet with a bit of space between them. Bake for 8–10 minutes, until the edges are just set and the centers still look slightly soft. Don’t wait for browning these are meant to stay light so the colors pop. Let the cookies cool on the baking sheet for a few minutes before transferring them to a wire rack. They will firm up as they cool.
Store in an airtight container at room temperature for up to 4 days if they last that long.
