Add in the sugar and beat for another 3 minutes on high.
Add in the egg and egg yolk and beat on high for another 2 minutes.
Beat in the vanilla.
Combine flour, baking soda, salt and spices in a bowl.
With the mixer on low add in the flour mixture. Mix for a minute and then finish with a spatula. You don't want to overwork the flour.
Refrigerate the dough for 1 to 2 hours.
Roll the dough out with flour to cut cookie shapes.
Bake for 7-10 minutes. Let them cool before you frost.
Royal Icing Recipe
Beat all of the ingredients above on high for a few minutes.
The goal of this frosting is to to get a consistency that won't spread when creating an outline, but blends perfectly for filling in the center... sounds easy right? If it's too thick add a little more water (like 1 teaspoon at a time) and if it's too thin add more powdered sugar.
Remove 1 cup of the frosting and set aside to dye red. The remaining white frosting can be placed in a pipping bag with a small round tip.
Place the red in a piping bag with an even smaller round tip.
To Decorate the Cookie
You have to work fast with this design because the frosting dries quickly. The white frosting needs to be wet in order to create this design. So I decorated one side of the cookie fully before moving to the next.
Outline and fill in one side with white frosting.
Make a zigzag line down the snowflake sides. Then, gently run a knife straight down the middle. That's it!
Notes
Recipe adapted from Dori Greenpan's book of Baking