In a large mixing bowl, whisk together the gluten-free flour, sugar, baking powder and salt.
Grate the frozen butter using a box grater. Add the butter to the flour mixture and combine with a pastry cutter, two forks or your fingers until the mixture resembles pea-sized crumbs.
Stir in the mix-ins to the flour mixture until evenly distributed. In a separate bowl, whisk together the sour cream and egg until combined.
Stir the sour cream mixture into the flour mixture with a rubber spatula until just combined and no dry flour streaks remain. Fold in the cheddar cheese.
Spread out a large piece of plastic wrap. Using wet hands, transfer the dough to the parchment paper. Clean and wet your hands again then pat the dough to form a 6-inch round that is 1-inch thick. Wrap the dough tightly in plastic and refrigerate for 30 minutes. (Do not refrigerate longer than 30 minutes.) Then, place in the freezer for 15 minutes while the oven preheats.
Preheat the oven to 500F. Line a baking sheet with a silicone mat or parchment paper.
After 15 minutes, take the dough out of the freezer. Spray a sharp knife with cooking spray and cut the dough into 6 equal wedges. Arrange the scones on the prepared baking sheet.
Place the scones in the oven, then immediately lower the oven temperature to 425°F. (You want the oven temperature to start hot so the scones turn golden brown as they cook through.) Bake for 12-14 minutes, until golden brown.
Remove from the oven. Transfer the scones to a wire rack and let cool for 20 minutes before topping with the garlic chive butter.
Whisk the garlic chive butter ingredients together. After cooling for 20 minutes, brush the tops of each scone with the butter.