Whisk together the flour, baking powder, and salt in a medium bowl; set aside.

Cream together the softened butter and granulated sugar in a large bowl until light and fluffy.

Beat in the egg and vanilla extract until well combined.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined and a soft dough forms.

Divide the dough in half, flatten each half into a disk, wrap in plastic, and chill for at least 30 minutes.

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

On a lightly floured surface, roll out one disk of dough to about 1/4-inch thickness, then cut out shapes using Christmas cookie cutters.

Place the cut-out cookies on the prepared baking sheets, leaving some space between them.

Bake for 8-12 minutes, or until the edges are lightly golden, then let cool completely on a wire rack.

In a large bowl, whisk together the powdered sugar, meringue powder, and warm water until smooth and thick.

Divide the royal icing into separate bowls and tint with gel food coloring as desired.

Decorate the cooled cookies with royal icing using piping bags or squeeze bottles, allowing the icing to set completely.

Optionally, add Christmas sprinkles, edible glitter, crushed candy canes, or small candies while the icing is still wet.