In a medium bowl, whisk together the all-purpose flour, baking powder, and salt. Set aside.

In a large bowl using a stand mixer or hand mixer, beat the softened butter and granulated sugar on medium-high speed until light and fluffy, about 3-4 minutes.

Add the egg and vanilla extract, beating until just combined.

With the mixer on low, gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix.

Divide the dough in half, shape into two flat disks, and wrap each tightly in plastic wrap.

Chill the dough in the refrigerator for at least 1-2 hours until firm.

Preheat oven to 375°F (190°C) and line baking sheets with parchment paper.

On a lightly floured surface, roll one disk of dough to 1/4-inch thickness. Cut into shapes using cookie cutters.

Place cookies on the prepared baking sheets and bake for 8-10 minutes, until the edges are lightly golden.

Let cool on the baking sheet for a few minutes before transferring to a wire rack to cool completely before decorating.

For the icing, whisk the powdered sugar and meringue powder together. Add the warm water and beat on low speed until combined, then on high speed for 2 minutes until stiff peaks form. Add more water, a teaspoon at a time, to reach desired consistency. Color with gel food coloring if desired.