Preheat the oven to 400 and prepare a cookie sheet with parchment paper. Set to the side.
In a medium-sized bowl, whisk flour, sugar, lemon zest, salt, and baking powder. Set to the side.
Next, use a box grater to grate the frozen butter into the dry ingredients. Combine the two mixtures using a pastry cutter or your fingers until the flour resembles a pea-sized crumb and is very dry.
In a small bowl, whisk the heavy cream, egg, and vanilla. Drizzle it over the flour and butter mixture and combine lightly, just until everything is incorporated. Fold in the blueberries. The mixture should be firm but still moist and sticky.
Pour the dough onto a floured surface and form into a loose ball. Don't worry if the dough is still sticky. If it looks a bit too sticky, add in a little more flour. However, if it seems too dry, add in 1-2 Tablespoons of heavy cream.
Shape the ball into an 8-inch disc. Cut the dough using a knife or a bench scraper, aiming for about 8 wedges.
Place scones on a prepared baking sheet with parchment about 2-3 inches apart. Brush scones with the remaining heavy cream and coarse sugar, if desired. This will give the scones an extra crunch when baking. Place the prepared scones in the refrigerator or freeze for 15 minutes.
After 15 minutes, place the scones in the oven for about 18-24 minutes. Keep an eye on the scones are remove them from the oven when they form a golden brown ring around the edge. The larger scones may take 25-30 minutes to bake.
While the scones are baking, make the glaze. Combine the lemon juice, heavy cream, and powdered sugar in a bowl. Whisk until desired consistency is reached.
When the scones are done, take them out of the oven and let them cool completely. Drizzle the glaze on top of them.
