In a large mixing bowl, whisk together the flour, sugar, baking powder, and salt until evenly combined. Add the cold, cubed butter and incorporate it into the flour mixture using a pastry blender or by rubbing the pieces between your fingertips until they resemble small, pea-sized crumbs. Gently fold in the blueberries and lemon zest.
In a separate small bowl, whisk together the heavy cream and egg until smooth. Pour the wet mixture over the dry ingredients, then use a silicone spatula or your hands to combine just until the dough is mostly moistened—it should remain slightly crumbly.
Lightly flour a clean surface and transfer the dough onto it. Knead gently a few times to bring it together into a ball. Press it into an even 8-inch circle, then slice into 8 equal wedges.
Arrange the scones on a small parchment-lined or silicone-lined baking sheet and place them in the freezer for 20 minutes. Meanwhile, preheat the oven to 400°F (200°C).
Transfer the chilled scones onto a large baking sheet, spacing them about 2 inches apart. Brush the tops lightly with additional heavy cream and sprinkle with sugar for a delicate crunch.
Bake for 20 to 25 minutes, or until the tops are lightly golden and the bottoms are a rich golden brown. Allow them to cool for at least 10 minutes before serving for the best texture and flavor.