Preheat the oven to 400°F (204°C) and line a heavy-duty baking sheet with parchment paper.

In a large chilled mixing bowl, whisk together the all-purpose flour, granulated sugar, baking powder, salt, and lemon zest until evenly distributed.

Add the cold, cubed butter to the dry ingredients. Use a pastry blender or two knives to cut the butter into the flour until the mixture resembles coarse crumbs with some pea-sized pieces of butter remaining.

In a separate small bowl, whisk together the 1/2 cup heavy cream, egg, and vanilla extract until smooth.

Create a well in the center of the dry ingredients and pour in the wet mixture. Use a silicone spatula to fold the ingredients together until a shaggy dough begins to form.

Gently fold in the fresh blueberries by hand, being careful not to crush the berries or overwork the gluten in the dough.

Transfer the dough onto a lightly floured surface. Gently pat and shape the dough into an 8-inch (20cm) circular disk, approximately 1 inch thick.

Using a sharp knife or bench scraper, cut the disk into 8 equal wedge-shaped pieces.

Place the wedges onto the prepared baking sheet, leaving at least 2 inches of space between each scone. For best results, chill the shaped scones in the freezer for 10 minutes before baking to firm up the butter.

Brush the tops of the scones lightly with the extra tablespoon of heavy cream and sprinkle generously with turbinado sugar.

Bake for 20 to 22 minutes, or until the edges are golden brown and the tops are slightly firm to the touch.

Transfer the scones to a wire rack and allow to cool for at least 10 minutes before serving.