Preheat the oven to 425°F and line a baking sheet with a silicone baking mat or parchment paper.
Combine the dry ingredients in a large bowl and whisk together. Add the cubed butter and cut in with a pastry cutter or two forks until it resembles coarse crumbs. Stir in ¾ cup buttermilk and mix until just combined.
Turn the dough out onto a floured surface and pat into a rectangle. Fold the rectangle into thirds and turn the dough a half turn. Flatten into a rectangle until the dough is about ½- to ¾-inch thick.
Cut the dough with a 2½-inch biscuit cutter and place the biscuits on the prepared baking sheet; the edges of the biscuits should be touching. Re-roll the dough as needed; there should be about 12 biscuits.
Refrigerate the biscuits at least 30 minutes to ensure the butter stays cold. This is especially important if your house/kitchen is warm and humid.
Brush the tops of the biscuits with the remaining 1 tablespoon buttermilk. Bake for 12-15 minutes or until the biscuits are browned and baked through.
• For best results, I highly recommend using Cup4Cup flour in this recipe. I used 274 grams of Cup4Cup and omitted the xanthan gum. • Be sure to cut the butter into the flour until the pieces of butter are fairly small. If the butter bits are too big, they won’t incorporate into the dough well and the biscuits will come out denser. • Try to work the dough as little as possible to keep the biscuits from being flat and tough.