Cream the shortening and sugar together in a mixer bowl or by hand. Add in the egg, sour cream, and vanilla and mix until combined.
In a separate bowl combine the flours and the xanthan gum. Whisk to aerate and combine. This is a very important step to ensure the starches and xanthan gum do not clump when added to the other ingredients.
Add in about ¾ of the flour mixture in 3 additions. Mix until incorporated after each addition. The dough should come together but still be sticky. Use the remaining flour mixture, as needed, when rolling out the dough.
Cut the dough in half and knead one half into a disk shape on a well-floured piece of parchment.
Roll the dough out to about ¼ inch thickness and cut out your cookies.
Carefully place cookies on a cookie sheet spaced about 2 inches apart. Cook in a 350 degree oven for 10 minutes until just starting to brown.
Continue with the other half of the dough. Re-roll the scraps and cut cookies out of those as well.
Cool on wire rack completely before icing.
Recipe by Glugle Gluten Free at http://glugleglutenfree.com/gluten-free-christmas-cookies/