Place 8 tablespoons (1 stick) of butter in 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), 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 better 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 flour a silicone baking sheet, wax paper, or a counter and put 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 scones to the prepared baking sheet.
Melt the last 2 tablespoons of butter and brush the tops of the scones.
Sprinkle the scones with decorator’s sugar, or another coarse sugar.
Place the scones into the preheated 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 the scones to cool for a few minutes on the baking sheet.
Move the scones to a cooling rack to finish cooling.
Make vanilla glaze, if using, by mixing all the ingredient together in a small mixing bowl until smooth and drizzle over blueberry scones.