Cream 1 cup of unsalted butter with 1 cup of granulated sugar using an electric mixer on medium speed for 3-4 minutes until light and fluffy.

Add 1 large egg, 1 teaspoon of vanilla extract, and a pinch of salt to the mixture and mix on low speed until fully combined for 1-2 minutes.

Whisk together 2 ½ cups of all-purpose flour and 1 teaspoon of baking powder in a separate bowl, then gradually add to the wet ingredients, mixing until a smooth dough forms.

Divide the dough in half; keep one half plain and color the other half with gel food coloring, mixing until the color is evenly distributed.

Combine small amounts of plain and colored dough in a bowl and gently knead to create swirls, achieving a marbled effect.

Shape the marbled dough into a disc, wrap in plastic wrap, and refrigerate for at least 30 minutes to 1 hour.

Roll the chilled dough to 1/4 inch thickness on a floured surface and cut out shapes with heart-shaped cookie cutters.

Place the cut-out cookies on a parchment-lined baking sheet and freeze for 15 minutes before baking.

Preheat oven to 350°F (175°C) and bake cookies for 12-14 minutes until edges are set, allowing to cool before transferring to a wire rack.