In a large bowl, whisk together your gluten free flour, xanthan gum, and salt until fully combined. This step spreads the salt and xanthan gum evenly so you don't end up with a patchy texture later. It only takes a minute, but it makes a real difference in the final bake.
Add your cold, cubed butter along with the freshly grated cheddar cheese to the flour mixture. Toss everything together with your hands or a spoon so the cheese and butter get coated in flour. This coating step helps prevent the dough from turning greasy once it bakes.
Create a small well in the center of your mixture and pour in the cold milk. Stir everything until it starts clumping together into a rough dough. If it feels too dry, add milk a teaspoon at a time until it holds together without crumbling apart.
Shape the dough into a flat disc, wrap it tightly in plastic wrap, and refrigerate it for about 20 minutes. Chilling firms the butter back up, which is what gives these crackers their signature flaky crunch once they hit the oven.
Unwrap your chilled dough and place it between two sheets of parchment paper. Roll it out to about ⅛-inch thickness, keeping it as even as you can. Use a pizza cutter to slice the dough into small, uniform squares.
Transfer your cut crackers onto a lined baking sheet and poke a small hole in the center of each one with a fork. Bake at 375°F for 12 to 15 minutes, flipping the tray halfway through so everything browns evenly. Let them cool completely on the pan, since they'll continue to crisp up as they sit.