Line a large baking sheet with parchment paper and preheat an oven to 400ºF.
Combine the buttermilk, sour cream and vanilla in a medium sized bowl and keep cool in refrigerator.
In another bowl combine the flour, baking powder, sugar and salt. Stir in the frozen grated butter with a fork then slowly pour in the buttermilk mixture until combined then, gently fold in the fresh blueberries.
On a floured surface form the dough into a large circle, about 10" in diameter. Cut into 8 triangular slice using a straight down cutting motion rather than slicing sideways. Place the slices a few inches apart on the parchment and bake for 17 to 20 minutes or until nicely golden on top.Leave to cool on a wire rack.
Leave to cool on a wire rack.
Course: Afternoon tea, Cakes and pastries, Dessert