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 chilled dough on a lightly floured surface to about ¼ inch thick (I use ⅜” if I know kids will be helping, because it makes the cookies sturdier). Cut out snowflake shapes and carefully transfer them to a parchment-lined baking sheet.

Snowflake cutters can have narrow points, so take your time lifting the shapes. If the dough gets soft or difficult to handle, return it to the refrigerator briefly before continuing.

Preheat your oven to 350°F (175°C). Bake for 8–10 minutes, or until the edges are just beginning to turn lightly golden.

Start checking at 8 minutes, especially if your snowflakes have thin points. Let the cookies rest on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.

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

Check the consistency by lifting the whisk. The icing should drizzle back into the bowl and smooth into the surface within about 5–10 seconds. Add the remaining water a little at a time as needed.

Keep the icing white for a snowy base that lets the blue and white sanding sugar stand out.

Transfer the white royal icing to a piping bag or icing bottle fitted with a small round tip. Outline each snowflake, then fill the center with more icing.

Use a toothpick or scribe tool to guide the icing into the points, fill small gaps, and pop any air bubbles.

While the icing is still wet, sprinkle the cookies with white and blue sanding sugar. You can use one color on each cookie or combine both for a frosty finish.

Decorate one or two cookies at a time so the sugar sticks before the icing begins to set. Sprinkle 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 additional drying time.