Preheat the oven to 400°F. Get out two large baking sheets; there's no need to grease them. If you have parchment, get out two pieces of parchment., Whisk together the dry ingredients, then work in the butter until the mixture is crumbly., Add the grated cheese and stir until thoroughly combined., In a separate bowl whisk together the egg and vinegar until frothy, then add the water., Add the wet ingredients all at once to the dry ingredients, mixing to make a cohesive dough. Add additional water a teaspoon at a time, if necessary to bring the dough together., Divide the dough into two pieces, and shape each into a rough square., Roll out one piece of dough at a time, keeping the piece you're not working with covered to prevent drying., Lightly dust your work surface, or a piece of parchment, with gluten-free flour blend., Roll the dough 1/4" thick, and cut into 1" squares, use a pizza or pastry wheel, a bench knife, or a plain knife. Prick each cracker with a fork., If you've rolled on parchment, simply lift the parchment onto the baking sheet. Separate the crackers a bit, leaving about 1/4" between them, so they crisp evenly. If you're not using parchment, transfer the crackers to the baking sheet, leaving about 1/4" between them., Repeat with the remaining piece of dough., Bake the crackers for 12 to 16 minutes, until their edges are starting to brown., Remove them from the oven, and cool right on the pan., Store cooled crackers in an airtight container, or tightly wrapped in plastic.