Prepare the pan. Line a large baking sheet with parchment paper. Preheat the oven to 400°F.
Combine the dry ingredients. In a large bowl, whisk together the flour, sugar, baking powder, salt, and lemon zest.
Cut in the butter. Add the cold cubed butter and use a pastry cutter or your fingertips to work it into the flour until the mixture resembles coarse crumbs with some pea-sized pieces of butter remaining.
Mix the wet ingredients. In a small bowl or measuring cup, whisk together the heavy cream, egg, and vanilla.
Make the dough. Pour the cream mixture into the flour mixture and gently stir until the dough is almost combined.
Add the blueberries and white chocolate. Gently fold in the blueberries and white chocolate. Don't overmix! The dough should look a little shaggy. If it seems excessively dry, add another tablespoon of cream.
Shape. Transfer the dough to a lightly floured surface and gently pat it into an approximately 7-inch round, about 1 inch thick. Cut into 8 wedges.
Chill. Place the wedges on the prepared baking sheet and refrigerate for 20 minutes. This little step helps keep those scones tall, flaky, and buttery.
Bake. Brush the tops lightly with heavy cream and sprinkle with coarse sugar. Bake for 18–22 minutes, or until puffed and golden around the edges.
Glaze. Let the scones cool for about 10–15 minutes. Whisk together the glaze ingredients until smooth and drizzle over the scones.