01 - Whisk together flour, baking powder, and salt in a medium bowl. Set aside for later use.
02 - Beat softened butter and granulated sugar in a large bowl until light and fluffy, approximately 2-3 minutes.
03 - Add egg and vanilla extract to the butter mixture. Beat until thoroughly combined.
04 - Gradually mix in dry ingredients until a soft dough forms. Be careful not to overmix.
05 - Divide dough in half and shape into discs. Wrap in plastic wrap and refrigerate for at least 1 hour.
06 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
07 - On a lightly floured surface, roll dough to 1/4-inch thickness. Cut heart shapes using cookie cutters.
08 - Place cut cookies 1 inch apart on prepared baking sheets.
09 - Bake for 8-10 minutes, or until edges begin to turn golden. Transfer to wire racks and cool completely.
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.
11 - Tint royal icing with gel food coloring as desired.
12 - Decorate completely cooled cookies with royal icing. Allow icing to set completely before serving or packaging.