Preheat the oven to 350°F (180°C). Line two cookie sheets with parchment paper or silicone mats and set aside.

Cream the butter and sugar using a stand mixer fitted with the paddle attachment. Beat on medium speed until smooth, light, and fluffy, about 2–3 minutes.

Add the vanilla and egg. Mix until just combined. Do not overmix.

Add dry ingredients. Mix in flour, baking powder, and salt. Scrape down the sides of the bowl with a spatula. The dough should pull away from the sides - if it’s too soft, add up to ½ cup more flour.

Roll out the dough. Divide into 4 portions and roll each one to ¼ inch (6 mm) thickness. Cut out cookies using an egg-shaped cutter and transfer to the prepared sheets using an offset spatula.

Bake for 8-9 minutes. Rotate the trays at the 6-minute mark for even baking. The edges should be just barely golden. Cool on the sheet for 5 minutes, then transfer to a wire rack to cool completely before decorating.

Mix icing. In a bowl, combine powdered sugar, meringue powder, and 6 tablespoons of water. Mix until just combined-do not overmix, or the icing may lose its shine. Add more water if needed, 1 teaspoon at a time.

Adjust consistency. For outlining, use a 15-second consistency icing. For flooding, use 8-10 second consistency. (To test: drag a knife through the icing and count how many seconds it takes to smooth out.)

Divide icing into bowls and add gel food coloring. Transfer to piping bags (with or without tips) and decorate cookies. Outline first, flood, then add designs once the base has set slightly.

Dry completely. Allow cookies to dry at room temperature for at least 2 hours-preferably overnight-before stacking or storing.