Cream the butter and sugar until light and fluffy. Add the egg and vanilla and mix well.

In a separate bowl, whisk together the flour and salt. Gradually add the dry ingredients to the wet ingredients and mix just until a soft dough forms.

Divide the dough in half, flatten each portion into a disk, and wrap in plastic wrap. Chill for at least 1 hour.

Roll the dough on a lightly floured surface to about ¼ inch thick. I roll it to ⅜ inch if kids are helping because the thicker cookies are sturdier.

Cut out the ornaments and transfer them to a parchment-lined baking sheet. If the dough gets too soft to lift cleanly, return it to the fridge briefly.

Preheat the oven to 350°F (175°C). Bake for 8–10 minutes, until the edges are just beginning to turn lightly golden. Let the cookies rest on the baking sheet for a few minutes, then transfer them to a wire rack to cool completely.

Sift the powdered sugar and meringue powder into a large bowl. Add 9 tablespoons of water and beat with a mixer fitted with a whisk attachment for about 1½–2 minutes.

Lift the whisk to check the consistency. The icing should drizzle back into the bowl and smooth into the surface within about 5–10 seconds. Add more water a little at a time as needed. Divide the icing among bowls and tint each portion a different color.

Transfer the icing to piping bags or icing bottles fitted with small round tips. Outline just the round part of each ornament, piping across where it meets the little top. Fill the outline with more icing and leave the top bare. Use a toothpick or scribe tool to fill small gaps and pop any air bubbles.

Add sanding sugar and let the cookies dry

If you’re using white sanding sugar, sprinkle it over the icing while it’s still wet. Work over a rimmed tray or a sheet of parchment to catch the excess.

Let the cookies dry uncovered for at least 6–8 hours or overnight before stacking or packaging. Thick icing or humid conditions may require more time.