Combine the flour, baking powder, salt and sugar together in a large bowl.
Grate in the frozen butter. Gently fold in the sour cream and vanilla.
Carefully combine the dough, being extra careful not to overmix it. The dough should be crumbly in texture.
Roll out the dough into a rectangular shape. Spread the blueberries over the dough. Roll dough into a log shape. Cut the scones into similar-sized wedges.
Place the scones onto a lined baking sheet, leaving space in between each one for rising. Brush the tops with a whisked egg, followed by a sprinkle of sugar.
Bake at 350°F for 30-40 minutes or until the scones are golden brown.