Gluten Free Icebox Cookies

The perfect buttery biscuit for any time of day. Keep the dough in the freezer so you'll always have a fresh bake, and no one will ever guess they are Gluten Free!
Prep Time: 15 Minutes
Chill Time: 8 Hours
Cook Time: 12 Minutes
Total Time: 8 Hour 30 Minutes
Special Equipment: Stand mixer or hand mixer
Ingredients:
150g caster sugar
160g rice flour
210g millet flour
1/2 tsp salt
2 tsp xanthan gum
227g butter, softened
1 tsp pure vanilla extract
1 large free range egg
sanding sugar or sprinkles for decoration
Directions:
In a stand mixer fitted with a paddle attachment, combine all of the dry ingredients and mix on low speed to combine.
Add the butter to the dry ingredients and continue to mix on low until fully incorporated.
Add the vanilla and the egg to the mixture, then mix on medium-high speed until the dough forms a ball.
Transfer the dough to a lightly floured work surface and knead the dough a few times to bring it together.
Shape the dough into 3 x 15 cm long logs with a 2.5 cm diameter.
Pour your sanding sugar or sprinkles out on a piece of parchment paper, then roll the logs in the sugar or sprinkles until the outside is evenly coated. Wrap the covered logs in plastic wrap and refrigerate for 8 hours.
When you are ready to bake, preheat your oven to 190 standard/170 fan/Gas 5 and line a baking sheet with parchment paper.
Remove one log of cookie dough from the fridge and cut 1 cm thick slices using a serrated knife. Place on the baking sheet and bake for 12 minutes until just starting to colour.
Store in an airtight container for up to 5 days. Any extra dough can be kept in the freezer for up to 3 months.
Tips:
If you want to decorate your cookies, mix together the zest and juice of one lemon with 100g powdered sugar and just enough water to make the icing spreadable. Use this to coat your cookies.
Demerara sugar is a great substitute if you don't have coloured sanding sugar or sprinkles.