For the Sugar Cookies:
Preheat the oven to 400 degrees F.
In a large bowl, sift the all-purpose flour and salt. Set aside.
In the bowl of a mixer fitted with a paddle attachment, cream the butter and sugar.
Once fluffy, add the egg and vanilla. Mix until just combined.
Add the dry ingredients. Mix until just combined.
Place the dough in a bowl, and allow it to rest for about 15 minutes. Do NOT refrigerate this dough. The cookies must be rolled out and baked right after the dough is made.
Line sheet pans with parchment paper or silicone baking mats.
Lightly flour a work surface and roll the dough out to about ¼ inch thickness. Cut out desired shapes and bake for about 7 to 8 minutes. If you'd like soft cookies, make sure that the cookies do not brown.
Once the cookies are baked, allow the cookies to cool on the baking sheets for about 5 minutes. Then transfer the cookies to a cooling rack to cool completely.
For the Royal Icing:
In the bowl of a mixer place the meringue powder and water. Whisk by hand for a few minutes until the powder is dissolved and the mixture bubbles.
Add the vanilla and hand whisk for an additional minute.
Place the bowl in the mixer fitted with a paddle attachment.
Add all the confectioners' sugar at once.
Mix on medium speed for about 5 to 7 minutes. You know the mixture is ready when it's white, fluffy, and stiff enough to hold peaks.
To Decorate the Cookies:
See the post above for instructions and photos!