01 - Whisk together flour, baking powder, and salt in a medium bowl. Set aside.
02 - Beat butter and granulated sugar in a large bowl until light and fluffy, approximately 2-3 minutes.
03 - Add egg and vanilla extract to butter mixture. Beat until thoroughly combined.
04 - Gradually mix dry ingredients into wet mixture until soft dough forms.
05 - Divide dough in half, shape into discs, wrap in plastic wrap, and refrigerate for minimum 1 hour.
06 - Preheat oven to 350°F. Line 2 baking sheets with parchment paper.
07 - Roll dough on lightly floured surface to 1/4-inch thickness. Cut heart shapes with cookie cutters.
08 - Place cookies 1 inch apart on prepared baking sheets.
09 - Bake for 8-10 minutes until edges are just turning golden. Cool completely on wire racks.
10 - Beat powdered sugar, meringue powder, and 3 tablespoons water until stiff peaks form. Adjust consistency by adding water a few drops at a time for piping or flooding.
11 - Tint royal icing with gel food coloring as desired.
12 - Decorate cooled cookies with royal icing. Allow icing to set completely at room temperature for several hours before serving or packaging.