Step 1

Preheat the oven to 375 degrees F (190 degrees C).

Step 2

Place flour, 1/2 cup sugar, baking powder, baking soda, and salt into a food processor. Pulse to combine. Add frozen butter and process until a fine crumb results and no hunks of butter are left.

Step 3

Transfer into the bowl of an electric stand mixer or a bowl for hand mixing. Add sour cream and egg. Set mixer on medium speed and blend until crumbs clump up and start to pull away from the sides of the bowl. Add blueberries and mix to combine.

Step 4

Take 1/2 of the dough and place on a floured surface. Shape with your hands, pushing blueberries in if they fall out, into a 1/2-inch thick disc, about 8 inches in diameter. Cut into 8 triangles and transfer to a baking sheet. Repeat with remaining dough. Sprinkle a pinch of sugar on each scone.

Step 5

Bake in the preheated oven until the tops start to turn golden, 17 to 22 minutes.