01 - Preheat the oven to 400°F. Line a baking sheet with parchment paper.
02 - In a large bowl, whisk together flour, sugar, baking powder, salt, and lemon zest until well combined.
03 - Add cold butter cubes. Using a pastry blender or fingertips, cut the butter into the flour mixture until it resembles coarse crumbs. Some pea-sized pieces should remain.
04 - Gently fold in the blueberries until evenly distributed throughout the mixture.
05 - In a small bowl, whisk together heavy cream, egg, and vanilla extract until blended.
06 - Pour the wet mixture into the flour mixture. Stir until just combined and dough begins to come together. Do not overmix.
07 - Turn the dough onto a lightly floured surface. Gently pat into a 1-inch thick circle. Cut into 8 wedges and transfer to the prepared baking sheet, spacing them evenly apart.
08 - Brush the tops with a little heavy cream. Bake for 18–20 minutes until golden brown on top. Cool on a wire rack.
09 - While scones bake, set up a double boiler: place a heatproof bowl over a saucepan of simmering water, ensuring the bowl does not touch the water.
10 - In the heatproof bowl, whisk together lemon juice, zest, sugar, eggs, and salt. Cook over simmering water, whisking constantly for 8–10 minutes until thickened enough to coat the back of a spoon.
11 - Remove from heat. Whisk in butter pieces one at a time until smooth and glossy. Let cool to room temperature.
12 - Serve scones warm or at room temperature with a generous dollop of lemon curd on the side.