01 - In a medium bowl, whisk together flour, baking powder, and salt. Set aside.
02 - In a large bowl, beat the butter and sugar until light and fluffy, about 2–3 minutes.
03 - Add the egg and vanilla extract; beat until well combined.
04 - Gradually mix in the dry ingredients until a soft dough forms.
05 - Divide dough in half, shape into discs, wrap in plastic wrap, and chill for at least 1 hour.
06 - Preheat oven to 350°F. Line 2 baking sheets with parchment paper.
07 - On a lightly floured surface, roll out dough to 1/4-inch thickness. Cut out heart shapes with cookie cutters.
08 - Place cookies 1 inch apart on prepared baking sheets. Bake 8–10 minutes, or until edges are just turning golden. Cool completely on wire racks.
09 - In a bowl, beat powdered sugar, meringue powder, and 3 tablespoons water until stiff peaks form. Add more water a few drops at a time for piping or flooding consistency.
10 - Tint icing with gel food coloring as desired. Decorate cooled cookies with royal icing. Let icing set completely before serving or packaging.