Preheat your oven to 400°F. Line a baking sheet with parchment paper or a silicone mat.
In a large bowl, whisk together the gluten-free flour, xanthan gum (if using), baking powder, sugar, and salt.
Add the cold, cubed butter to the dry ingredients and use a pastry cutter or two forks to cut the butter into the flour mixture until it resembles coarse crumbs.
Pour in the ice cold water and use a fork to gently mix the dough until it comes together into a shaggy ball. Turn the dough onto a lightly floured surface and knead gently for about 1 minute until smooth. Wrap in plastic wrap and chill for 45-60 minutes in the fridge.
Roll out the dough into a rectangle, approximately 1/4 inch thick.
Using a sharp knife or cookie cutter, cut the dough into rounds, squares or rectangles, about 2 inches in size.
Transfer the cut crackers to the prepared baking sheet, spacing them about 1 inch apart. Prick the top of each cracker with a fork to create a decorative pattern.
Bake the crackers for 12-15 minutes, or until they are lightly golden brown and crisp.
Remove the crackers from the oven, brush with (optional) melted butter and sprinkle with salt if desired, and let them cool completely on the baking sheet.
Serve and enjoy.
Notes
Make sure the butter is cold, and the water is ice cold before mixing with the other ingredients.
Don't overcrowd the baking sheet—you'll likely need to bake these crackers in batches.
The dough can be prepared up to 2 days ahead of time before baking. Keep it in the fridge wrapped in plastic wrap until ready to use.
To Store: Keep in an airtight container for up to 5 days at room temperature.
To Freeze: Store in a freezer-safe bag or container for up to 3 months. Let the crackers thaw at room temperature.