Combine the dry ingredients. In a large bowl, whisk together the gluten-free flour, sugar, baking powder, and salt until well-combined. If you're using a food processor, pulse the dry ingredients a few times to mix them.
Add the frozen butter. Grate the butter on a box grater and add it to your flour mixture. Using a pastry blender or two forks, quickly work the butter into the flour until the mixture resembles coarse crumbs. If you're using a food processor, add diced frozen butter to the bowl and pulse until coarse crumbs form.
Whisk the wet ingredients. In a separate bowl, whisk together the sour cream, one large egg, heavy cream, and vanilla extract until the mixture is smooth and combined.
Create a well in the center of the flour mixture. If you used a food processor, transfer the contents to a large bowl. Create a well in the center of the dry ingredients and pour the sour cream mixture into it.
Stir the wet and dry ingredients. Using a rubber spatula, carefully mix the ingredients just until a shaggy, coarse dough comes together. Don't be concerned if it appears loose or if there are a few dry bits at the bottom of the bowl; as long as the dough clings together when you pinch it, you've got it right. It's important not to overmix the dough.
Add the mini chocolate chips. Gently fold the mini chocolate chips into the dough until they are evenly distributed.
Bring the dough together. Turn the dough onto a lightly floured surface. Using floured hands, gently knead it just until it comes together. Avoid overworking the dough, as this will make your scones tough.
Shape the dough. Gently pat the dough into a 7x5-inch rectangle. Using a knife or a bench scraper, cut the dough in half vertically. I prefer using a bench scraper, as it makes it easy to cut and lift the dough without warming it up too much.
Create flaky layers by laminating the dough. Stack the two pieces on top of each other. Turn the stacked dough 90 degrees and gently press it back into a 7x5-inch rectangle. If the dough starts to feel sticky, lightly flour your hands or work surface.
Repeat lamination. Repeat the entire process of cutting, stacking, and rotating a total of four times.
Shape the dough into a disk and chill. Shape the dough into a 7-inch disk, about an inch thick, using your hands. Make sure it isn't thinner than ¾ inch, or the scones might be flat. Wrap the disk tightly in plastic wrap and chill it in the refrigerator for at least 30 minutes. This step is crucial because it allows the gluten-free flour to fully absorb the liquid, ensuring your final scones have a smooth, less gritty texture.
Cut the scones. After the dough has chilled, take it out of the refrigerator. Using a sharp knife or bench scraper, slice the disk into eight triangular wedges. For the cleanest cut and best rise, make sure to press straight down through the dough without twisting. You can also wipe the knife clean after each slice.Freeze the scones and preheat the oven. Arrange the cut scone wedges on a parchment-lined baking sheet, leaving a few inches of space between each. Place the baking sheet in the freezer for 30 minutes. While they're chilling, preheat your oven to 400°F. This final chill is the key to achieving a flaky, high-rising scone, as it ensures the butter stays very cold right before it hits the heat. Prepare the egg wash. After the scones have chilled for 30 minutes, remove them from the freezer. In a small bowl, whisk together one large egg and a splash of heavy cream. This egg wash will help the scones achieve a beautiful, golden-brown finish as they bake.
Add the egg wash and sugar. Using a pastry brush, gently brush the egg wash over the tops of the scones. Be careful to avoid any drips on the sides, which can hinder the rise. Finish by sprinkling the tops with granulated sugar.
Let's bake! Place the baking sheet in the preheated oven and bake for 19-20 minutes, or until the scones are a beautiful golden brown. To test for doneness, you can insert a toothpick into the center—it should come out clean—or use an instant-read thermometer, which should read at least 200°F. Once baked, remove the scones from the oven and transfer them to a wire rack to cool for at least 30 minutes before serving.