Preheat oven to 400°F (200°C) and line a baking sheet with parchment paper.,In a large bowl, whisk together flour, sugar, baking powder, salt, and lemon zest.,Cut in cold butter using a pastry cutter or fingers until mixture resembles coarse crumbs.,Gently fold in blueberries.,In a separate bowl, whisk heavy cream (or milk), egg, and vanilla until smooth.,Pour wet mixture into dry ingredients and stir just until combined, avoiding overmixing.,Drop large tablespoons of dough onto prepared sheet, spacing about 2″ apart.,Sprinkle tops with coarse sugar if using.,Bake 15–18 minutes, or until scones are golden and set.,If making glaze, whisk powdered sugar, lemon juice, and zest until smooth.,Drizzle glaze over warm scones once they’ve cooled slightly.