• If you're making drop biscuits preheat your oven to 425°F. If you're making rolled biscuits, preheat your oven while the shaped dough is chilling in the refrigerator.
• Line a large rimmed baking sheet with unbleached parchment paper and set it aside.
• In a large bowl, place the flour blend, xanthan gum, cornstarch, baking powder, baking soda, salt, and sugar, and whisk to combine well.

To make drop biscuits

• Using a standard box grater, grate the chilled butter. If it melts at all during preparation, place the grated butter in the refrigerator until firm.
• Add the grated and chilled butter to the bowl of dry ingredients, and toss to coat the butter in the flour mixture.
• Create a well in the center of the dry ingredients, add the buttermilk and mix until just combined.
• Working quickly, so the dough doesn’t get warm, drop the batter by the quarter cup using two large spoons or a 2-inch ice cream scoop about 1 1/2-inches apart on the prepared baking sheet. Do not pack the dough into the ice cream scoop.
• Brush the tops of the mounds of dough lightly with the melted butter. This step is optional but helps the biscuits brown in the oven.
• Place the baking sheet in the center of the preheated oven and bake until lightly golden brown all over (15 to 18 minutes). Remove from the oven and allow to set briefly before serving.

To make rolled biscuits

• Using a sharp knife, cut the butter into a large (3/4-inch) dice. If it melts at all during preparation, place the diced butter in the refrigerator until firm.
• Add the chopped butter to the flour mixture and toss to coat. Place each piece of butter between your floured thumb and forefinger to flatten, working quickly to ensure that you don’t melt any of the butter.
• Create a well in the center of the dry ingredients, and pour in all but about 2 tablespoons of the buttermilk.
• Mix with a large spoon or spatula until the dough comes together. The dough will be shaggy, with some irregular edges. Mix in more buttermilk by the drop if there are any dry bits.
• Press the dough into a disk. If it doesn't seem cold any longer, place it in the refrigerator to chill for about 5 minutes or until firm.
• Dust the dough with a bit more flour, and roll with a rolling pin into a rectangle about 3/4-inch thick.
• Fold the rectangle in thirds like you would a business letter and press it together lightly to help it adhere to itself.
• Sprinkle the outside of the dough lightly with more flour, and roll it out again into a thick rectangle, sprinkling it with more flour as necessary to prevent sticking.
• Repeat this process of rolling and folding 1 or 2 more times, dusting with flour as necessary and chilling the dough if the butter begins to melt at all. After the final folding, dust the dough again lightly with flour, and roll it into a disk about 1-inch thick.
• With a floured, round biscuit cutter or cookie cutter (about 2 inches in diameter), cut out rounds of dough by pressing firmly and cutting quickly.
• Place the raw biscuit cutouts about 2-inches apart from one another on the prepared baking sheet. Gather and reroll scraps, and cut out as many more rounds as possible, placing them on the prepared baking sheet.
• Place the baking sheet in the freezer for 5 minutes to chill the dough until firm (or in the refrigerator for 10 minutes or until firm).
• Preheat your oven to 425°F while the biscuits are chilling.
• Once the dough is firm and cold, and the oven is hot, place the baking sheet in the center of the preheated oven. Bake until the biscuits are puffed and pale golden, about 15 minutes.
• Remove the baking sheet from the oven and allow the biscuits to cool on the baking sheet until firm (about 5 minutes). Serve warm or at room temperature.