In a large mixing bowl, cream butter and sugar.
Add the egg, vanilla, cinnamon, and salt, and blend.
Add the flour and mix until smooth and combined. Cover the dough, and refrigerate for at least 1 hour.
Take the dough out of the fridge, and let it warm up to soften a bit on the counter. If you left the dough in the fridge for just an hour, you can start kneading right away until the dough feels pliable to roll. If you left your dough in the fridge overnight and the butter is hard, let the dough come to room temp for a good 30 minutes before kneading.
Pre-heat the oven to 350 degrees, and line a baking sheet with unbleached parchment paper or Silpat.
Dust your counter with some gluten free flour, knead the dough so it is pliable, and roll the dough out to about 1/4 inch.
Use a cookie cutter to cut out your shapes, and bake at 350 degrees for 13-15 minutes.
Let the cookies cool completely before decorating. To make the frosting, just blend the frosting ingredients until smooth. You can add more milk if you wish for a thinner, more royal icing type of frosting. If you're using the natural dyes for the frosting, separate the frosting into small bowls, and then stir in the colors. The frosting will harden as it dries.