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, mixing until fully incorporated.
04 - Gradually add dry ingredients to wet mixture, beating on low speed until dough forms.
05 - Divide dough in half, flatten into discs, wrap in plastic, and refrigerate for at least 1 hour.
06 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
07 - On lightly floured surface, roll dough to 1/4 inch thickness. Cut heart shapes and place 1 inch apart on prepared baking sheets.
08 - Bake for 8–10 minutes until edges begin to turn golden. Cool on baking sheet for 5 minutes, then transfer to wire rack to cool completely.
09 - Combine powdered sugar and meringue powder. Add 3 tablespoons water and beat on low speed until stiff peaks form, about 5 minutes. Adjust consistency with additional water if needed.
10 - Divide icing and tint with gel food coloring as desired. Transfer to piping bags for decorating.
11 - Decorate cooled cookies with royal icing. Let set at room temperature until dry, approximately 1 hour.