Preheat your oven to 200C and line 2 baking sheets with baking parchment. Set aside.
In a large measuring jug combine the milk, sour cream, egg and vanilla extract. Whisk everything together and set aside.
In a large mixing bowl stir the flour, baking powder, bicarb and sugar together. Add the cold butter to the flour mixture and using your finger tips rub the butter into the flour until the mixture resembles breadcrumbs. Toss the blackberries in the flour, making sure to coat the blackberries in the mixture.
Pour the egg mixture into the flour and butter and using a fork mix together until you get a shaggy dough. Dump the dough out onto your counter top and working quickly scrunch the dough together into a circle around 1 inch thick.
Using a sharp knife cut the dough into quarters then half each quarter to give you 8 triangles. Transfer the scones to the prepared baking sheets, 4 per sheet. Brush each scone with the milk and sprinkle on a little demerera sugar.
Bake for 20 – 25 minutes until golden brown. Allow to cool on the tray for 10 minutes before transferring to a wire rack to finish cooling.
To make the glaze combine the icing sugar, vanilla extract and 1tbsp milk in a bowl and mix to form a thick glaze. If it’s a little too thick add a tiny splash more milk until you reach the desired consistency.
Spoon the glaze over the scones and top with a fresh blackberry.