½ teaspoon clear vanilla extract (you can use regular vanilla extract,but I like clear because it won't tint the white color)
5-8tablespoonswater,or more depending on desired consistency (see primer above for more information)
Instructions
Make the buttery sugar cookie dough
In the bowl of an electric stand mixer fitted with the paddle attachment, cream the butter, granulated sugar and sifted confectioners' sugar together on low speed for about 5 minutes until light and fluffy. You do not want to aerate.
Gradually add the egg yolks one at a time ensuring each one is well incorporated before adding the next. Add the vanilla extract. Scrape down the bowl and the paddle.
On low, slowly add the flour and salt and mix until the dough comes together into a ball.
Transfer the sugar cookie dough to a lightly floured surface and form into a disc. Refrigerate for at least 30 minutes to 1 hour before rolling out.
Preheat oven to 350F. Roll out the dough to ¼" and cut out shapes using a cookie cutter. Transfer the shapes to a parchment paper-lined baking tray leaving about an inch in between. Let chill in the freezer for 15 minutes. This will help prevent the cookies from spreading. Bake 10-13 minutes, rotating halfway.
Make the royal icing
In the bowl of an electric stand mixer fitted with the whisk attachment, combine all the ingredients (start with 5 tablespoons of water and add more as you go) and mix on low until incorporated. Then increase the speed to medium-low until and mix until icing begins to form peaks, about 5-7 minutes.
Add more water, one tablespoon at a time until you've reached your desired consistency. See notes above about royal icing consistencies.