In a large bowl combine all dry ingredients (flour, sugar, baking powder, and salt).
Using a fork, or by hand add in the cold butter cubes and work into the dough. Make sure not to overwork - dough should resemble a pie crust dough, as not to have the butter melt. Chunks of dough should not exceed a cranberry in size.
In a separate bowl (or in the measuring cup), combine buttermilk (if no buttermilk on hand, use regular milk + 1 tbsp of vinegar - allow to sit for 5 minutes), egg, lemon zest, extract, and vanilla.
Add the blueberries to the dry ingredients.
Add wet ingredients to the bowl, and stir until just moistened. You want the dough to look shaggy, and rough. Do not overwork it. Once the dough looks moistened, turn it over onto a floured surface on the counter.
Shape dough into an 8" disc, about 2" in height. Slice into 8 pieces/ Place 2" apart on a parchment lined baking sheet and brush with a tsp of buttermilk/milk.
Set in fridge for 15 minutes. Preheat oven to 400° in meantime.
Bake for 20-25 minutes, until golden brown. Allow to cool before adding glaze.
While baking, combine confectioners sugar, lemon zest, and lemon juice to make the glaze. Using a spoon drizzle the glaze on the cooled scones.