Preheat the oven to 350°F (175°C). Line a large baking sheet with parchment paper or a silicone baking mat and set aside.
In a large bowl, cream the butter and sugar together until light and fluffy. Add in the egg and vanilla extract, mixing until the batter is smooth and fully combined.
Stir in the flour, baking soda and baking powder, until a soft dough forms. If the dough feels dry or crumbly, mix in 1 tablespoon of melted butter to help bind it together.
Divide the dough evenly into three parts. Leave one portion uncolored. Tint the other two with red and blue food coloring, mixing each until the color is evenly distributed.
Pinch off about a tablespoon of dough from each color and gently press them together. Roll lightly between your hands to form a marbled cookie ball with a tie-dye pattern.
Roll each cookie ball in a little granulated sugar, then arrange them on the prepared baking sheet, leaving room for spreading.
Bake for 12 to 15 minutes, or until the edges are just turning golden. The centers should remain soft and slightly puffy.
Let the cookies cool on the baking sheet for a few minutes, then transfer to a wire rack to cool completely before serving.
Notes
Gel food coloring works best to get bright, bold colors without changing the texture of the dough.
To keep the tie dye effect, avoid over mixing the colored dough pieces once they’re combined.
If baking with kids, let them help with the swirling and rolling—it’s a fun, mess-friendly activity!