Preheat oven to 400 degrees (F) and set oven rack to the middle position. Line a baking sheet with parchment paper and set aside.
In a medium-sized bowl, gently toss flour, baking powder, baking soda, and salt. Set aside.
In a separate small bowl, whisk sour cream and egg until completely smooth. Set aside.
In a large bowl, stir sugar and orange zest together until sugar is moistened and zest is evenly distributed. Pour in flour mixture and toss to combine.
Grate frozen butter into mixture using a medium grater. Using your hands, work in the butter until the mixture resembles a coarse meal. Gently stir in sour cream mixture until just about combined. Do not overwork the dough.
Very gently press the dough against the sides of the bowl a few times and form a ball. The dough will be sticky at first but will come together as you form it.
Place dough on a lightly floured surface and gently pat into an 8-inch circle about 3/4-inch thick. Use a very sharp knife to cut into eight triangles (like a pizza). transfer triangles onto prepared baking sheet, leaving about 1 inch between.
Bake scones for 15 - 17 minutes or until the tops begin to turn golden. Don't take them out too early or they will be too soft. Allow them to cool for 10 minutes on the baking sheet before transferring to a wire rack to finish cooling completely.
While the scones bake, prepare the glaze. Melt butter in a glass dish in the microwave for 30 seconds. Whisk in the powdered sugar, vanilla, and orange juice until smooth.
Once completely cooled, drizzle the glaze on the scone tops and sides with a spoon.
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