Place 8 tablespoons (1 stick) of butter in the freezer.
Preheat an oven to 400⁰F.
Sift flour and baking powder into a large mixing bowl.
Add the sugar to the flour and stir to combine.
In a small bowl add the egg, yogurt (or sour cream), and vnailla, along with the heavy cream or milk and stir to combine. Set aside.
Remove the butter from the freezer and grate, using the small holes on a grater, into the flour and sugar mixture.
Toss the butter in the flour mixture until the butter is coated. Separate any clumps of butter as best as you can until there are no large lumps of butter left.
Rub the flour and butter with your fingers until it forms coarse crumbs.
Pour the egg mixture over the flour and butter and stir just until everything is moist. Do not overwork the dough.
If the dough will not come together by squeezing or patting, add cream or milk 1 tablespoon at a time until it does.
Add the blueberries and gently stir to combine, trying not to break too many blueberries.
Liberally sprinkle additional flour on a silicone baking sheet, wax paper, or a counter and put the dough on it.
Lightly sprinkle the top of the dough with flour and gently knead the dough a few times, trying not burst open the blueberries.
Form the dough into an 8-inch circle and cut into 8 equal pieces.
Line a baking sheet with silicone baking sheet or parchment paper. Alternatively, a baking sheet sprayed liberally with baking spray can be used.
Carefully move the pieces to the prepared baking sheet.
Melt the last 2 tablespoons of butter and brush the tops and sprinkle with coarse sugar if using.
Place into a 400°F oven and bake for 20 to 25 minutes or until the scones have started to brown and the blueberries are bubbling.
Remove from the oven and allow to cool for a few minutes on the baking sheet.
Move to a cooling rack to finish cooling.
Vanilla Glaze
Make the vanilla glaze, if using, by mixing all the ingredients together in a small mixing bowl until smooth and drizzle over the top.
Notes
Frozen blueberries can be used, do not thaw first.
Start with super cold butter, a few minutes in the freezer is helpful
Do not overwork the dough
Only use as much liquid as needed to hold the dough together
Gently shape the dough using light finger and hand pressure, avoid a rolling pin.
Do not overbake scones, they are meant to be cooked but moist in the middle
Freeze unbaked scones. Remove from the freezer and bake for an addition 3 to 5 minutes.
Nutritional data includes sugar topping and vanilla glaze.