Combine the granulated sugar and lemon zest in a large bowl, rubbing them together until the mixture looks like coarse sand.
Add the flour, baking powder, and salt to the lemon sugar mixture and whisk together. Grate the cold butter into the flour mixture in 2-3 tablespoon increments, tossing to coat the butter pieces with flour.
Using your fingers or a pastry cutter, blend the butter into the flour until the mixture has the texture of coarse sand with some pea-sized bits.
In a separate bowl, whisk the egg, then stir in the cold heavy cream, lemon juice, and vanilla extract until fully combined.
Make a well in the center of the dry ingredients, add half of the wet mixture, and gently fold to combine. Pour in the remaining wet ingredients and fold just until the dough comes together, leaving a few small pieces.
Gently fold in the blueberries without breaking them up.
Turn the dough onto a lightly floured surface and shape it into a ball. Press the dough down to form a disk, fold it in half, and press into a disk again. Aim for an 8-inch diameter disk.
Place the disk on a parchment-lined baking sheet or plate and chill in the freezer for 30-40 minutes. Meanwhile, preheat the oven to 400 F (204 C).
Remove from the freezer and cut the disk into 6-8 wedges with a dough scraper or sharp knife. Arrange scones 2 inches apart on a lined baking sheet and brush the tops with heavy cream.
Bake the scones for 18-22 minutes until golden brown and fragrant. Let them cool on the baking sheet for 3-4 minutes, then transfer to a wire rack.
While the scones cool, prepare the lemon glaze by mixing powdered sugar and lemon juice to a drizzling consistency. Drizzle the glaze over the cooled scones and serve.
