In a large bowl, cream the butter and powdered sugar (2-3 minutes). Beat in egg and vanilla. Combine the flour, baking powder, and salt in a separate bowl. Add the dry ingredients to the butter mixture and mix until combined.

Divide the dough in half; use the food coloring to tint one portion pink, and leave the remaining portion white. Wrap each portion in plastic wrap and refrigerate for at least 4 hours (or overnight).

Preheat the oven to 350°.

For each cookie, shape a 1-inch ball of each color into an 8-inch rope. Place a pink and white rope side-by-side; press together gently and twist. Place it on a baking sheet and shape it into a heart, pinching the ends to seal (at the bottom of the heart).

Bake for 8-11 minutes or until edges are lightly browned. Let the cookies cool on the baking sheet for a few minutes before transferring the cookies to a wire rack to cool completely.