Bittersweet chocolate is the kicker in these tempting gluten-free scones. Dunk them in mugs of steaming coffee and prepare to be wowed.
Preheat oven to 400°.
Weigh or lightly spoon flours into dry measuring cups; level with a knife. Combine flours, 1/2 cup sugar, and next 4 ingredients (through salt) in a medium bowl, stirring with a whisk; cut in butter with a pastry blender or 2 knives until mixture resembles coarse meal. Stir in chocolate.
Combine 1/2 cup buttermilk and egg in a small bowl; stir with a whisk. Add to flour mixture; stir just until moist.
Turn dough out onto a surface lightly dusted with white rice flour. Pat dough into an 8-inch circle; cut into 10 wedges. Place wedges on a baking sheet lined with parchment paper. Brush 1 tablespoon buttermilk over surface of dough; sprinkle with 1 teaspoon sugar.
Bake at 400° for 18 minutes or until golden brown. Remove scones from baking sheet to a wire rack. Serve warm.