• Line a rimmed baking sheet with unbleached parchment paper and set it aside.

Make the dough

• In a large bowl, place the gluten free flour blend, xanthan gum, cornstarch, baking powder, and salt, and whisk to combine.
• Add the diced butter, and toss to coat it in the dry ingredients. Flatten each piece between your fingers to create thin shards.
• Add the shredded cheese, and toss to coat the shreds in the dry ingredients. Create a well in the center of the dry ingredients.
• Add the cold buttermilk, and mix lightly to combine. The mixture should come together and everything should be just moistened in clumps.
• If there are very crumbly bits, still, after mixing, add cold water by the teaspoon right on the dry parts. Mix again, and repeat as necessary.

Shape

• Transfer the dough to a lightly floured surface. With clean, dry hands, lightly pat it into a rough rectangle. Sprinkle the top lightly with more flour.
• Use a rolling pin to roll it out into a rectangle about 12-inches x 6-inches and about 1/2-inch thick.
• Using a floured metal bench scraper or sharp knife, cut the dough into 3 equal 4-inch x 6-inch rectangles. Stack the rectangles on top of one another, and press down to help the dough stick.
• Rotate the stack so a short end is facing you, roll the dough into a rectangle again, but this time about 10 inches x 5 inches. Slice in half, stack in a 5-inch square, and press the layers together to adhere.
• Press in the corners to round them, and roll the dough into a round about 8 inches in diameter using your hands and a rolling pin. Flour the pin, surface, and dough lightly to prevent sticking.
• Use a sharp knife or bench scraper to cut the round into 8 triangles by slicing it through the center at right angles, then slicing each resulting quarter into 2 triangles.

Chill the dough

• Separate the triangles from one another, and place the raw scones on a cutting board or other small, flat portable surface.
• Freeze the shaped scones for 15 to 30 minutes, or until firm. While the dough is chilling, preheat your oven to 375°F.

Bake the scones

• Place the chilled scones on the prepared baking sheet about 1 inch apart from one another. Brush the tops with cream and sprinkle with coarse salt, if using.
• Place the baking sheet in the center of the preheated oven. Bake until the scones are puffed and firm to the touch, and brown on the edges (18 to 20 minutes). Some of the cheese will have leaks out the sides and turned lacy and super crispy.
• Remove the baking sheet from the oven. Allow the scones to set briefly on the baking sheet before serving.