Prepare the Dough:

1. Mix Dry Ingredients: In a medium bowl, whisk together the flour, baking powder, and salt. Set aside.
2. Cream Butter and Sugar: In a large mixing bowl, beat the softened butter and sugar together until light and fluffy, about 2-3 minutes.
3. Add Wet Ingredients: Mix in the egg, vanilla extract, and milk until well combined.
4. Combine with Dry Ingredients: Gradually add the flour mixture, mixing until a soft dough forms. Do not overmix.
5. Chill the Dough: Shape the dough into a disk, wrap it in plastic wrap, and refrigerate for at least 1 hour. This helps the cookies hold their shape when baked.

Roll and Cut the Cookies:

6. Preheat the Oven: Set your oven to 350°F (175°C). Line a baking sheet with parchment paper.
7. Roll the Dough: On a lightly floured surface, roll out the dough to about ¼-inch thickness.
8. Cut Out Shapes: Use a heart-shaped cookie cutter to cut out cookies and place them on the prepared baking sheet.
9. Bake the Cookies: Bake for 8-10 minutes, or until the edges are just lightly golden. Do not overbake.
10. Cool Completely: Let the cookies rest on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.

Decorate the Cookies:

11. Prepare the Icing: If using royal icing, mix powdered sugar with a little water or milk until you reach a smooth, pipeable consistency. Add food coloring if desired.
12. Decorate: Use a piping bag or a spoon to spread the icing on the cooled cookies. Add sprinkles, sanding sugar, or edible glitter for extra charm.
13. Let the Icing Set: Allow the cookies to sit at room temperature until the icing hardens.