In a large bowl, cream the sugar and butter at medium speed.
Add the egg, water, vanilla, salt, and cinnamon (if using). Blend until mixed well.
Add the xanthan gum (if using) and flour. Mix at a low speed until well combined.
Cover and refrigerate for at least 1 hour.
Preheat the oven to 350F. Line a baking sheet with parchment paper and set it aside.
Roll out the dough onto a lightly floured surface, about ¼-inch thick.
Cut out the dough with selected cookie cutters, and place the cookies on the baking sheet. Make sure the cookies are not touching.
Reform and roll out the scrap dough, then continue cutting more cookies.
Bake for 10 to 12 minutes. Remove from the oven, and let the cookies cool for 5 minutes on the cookie sheet before removing them to a cooling rack. Cool completely before decorating.
Store in an airtight container for up to 5 days.
Notes
Not all gluten-free flours are the same. I've listed the all-purpose flours that I've used with this recipe and yielded great cookies.
Refrigeration is a must, otherwise, your dough will be too sticky to roll, and the cookies will spread. If you roll out your dough, and it's too sticky to pick up, put it back in the fridge before cutting.
Gluten-free flour absorbs less moisture compared to regular flour. As with any gluten-free recipe, using the same amount of flour provided in the recipe is recommended, and substitutions are highly discouraged.