Preheat your oven to 425°F (220°C). Line a baking sheet with parchment paper.

In a large mixing bowl, whisk together the gluten-free all-purpose flour blend, baking powder, baking soda, salt, and granulated sugar (if using).

Add the very cold, cubed butter to the dry ingredients. Use a pastry blender, two forks, or your fingertips to cut the butter into the flour mixture until it resembles coarse crumbs with some pea-sized pieces of butter remaining. This is crucial for flaky biscuits.

Pour in the cold buttermilk. Use a spatula or wooden spoon to mix until just combined and a shaggy dough forms. Be careful not to overmix. If the dough seems too dry, add buttermilk one tablespoon at a time until it just comes together.

Turn the dough out onto a lightly floured (with GF flour) surface. Gently pat the dough into a rectangle about 3/4 to 1 inch thick. Avoid overworking the dough, as this can make biscuits tough.

Using a 2.5-inch biscuit cutter, cut out biscuits, pressing straight down without twisting. Twisting seals the edges and can prevent them from rising properly. Gather the scraps, gently re-pat them together, and cut out any remaining biscuits.

Arrange the biscuits on the prepared baking sheet, allowing them to touch slightly for softer sides, or spaced apart for crispier edges. Bake for 12-18 minutes, or until golden brown on top and cooked through.

For extra richness and a golden shine, brush the tops of the hot biscuits with melted butter immediately after removing them from the oven. Serve warm with butter, jam, or gravy.