Mix dry ingredients: In a large bowl, whisk together the flour, sugar, lemon zest, baking powder, and salt.
2 cups all purpose flour plus extra for dusting, 6 tablespoons granulated sugar, 1 tablespoon fresh lemon zest, 2 1/2 teaspoons baking powder, 1/2 teaspoon salt
Grate butter: Shred the frozen butter into the bowl using a box grater. Cut it into the flour with a pastry cutter or forks until coarse crumbs form. Place the bowl in the freezer to keep everything cold.
1/2 cup unsalted butter frozen
Combine wet ingredients: In a small bowl, whisk 1/2 cup of the heavy cream with the egg and vanilla.
9 tablespoons cold heavy cream divided, 1 large egg cold, 1 1/2 teaspoons vanilla extract
Form dough: Pour the wet mixture into the dry mixture. Add blueberries and gently mix just until moistened. Do not overmix.
1 heaping cup fresh blueberries
Shape dough: Turn onto a lightly floured surface and press together into a rough ball. Pat into an 8-inch round disc about 1 inch thick.
Cut scones: Slice into 8 wedges and transfer to a parchment-lined baking sheet.
Brush and chill: Mix the remaining 1 tablespoon cream with the water and brush the tops. Sprinkle with coarse sugar if desired. Chill for at least 15 minutes so the butter stays cold and the scones bake up flaky.
1 tablespoon water, Coarse sugar optional
Bake: Bake at 400°F for 22 to 25 minutes until lightly golden.
Make glaze: Whisk powdered sugar and lemon juice until smooth.
1 cup powdered sugar, 3 tablespoons fresh lemon juice
Finish: Drizzle glaze over slightly warm scones and let set before serving.