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 to the flour mixture. Using a pastry blender or your fingertips, cut the butter into the flour until the mixture resembles coarse crumbs with some pea-sized pieces remaining.
04 - Gently fold in the fresh blueberries until evenly distributed throughout the flour mixture.
05 - In a small bowl, whisk together heavy cream, egg, and vanilla extract until fully blended.
06 - Pour the wet ingredients into the flour mixture. Stir gently with a spatula or wooden spoon until just combined. The dough should be slightly shaggy but hold together. Avoid overmixing.
07 - Turn the dough onto a lightly floured surface. Gently pat into a 1-inch thick circle. Cut into 8 equal wedges using a sharp knife or bench scraper. Transfer wedges to the prepared baking sheet, spacing them 2 inches apart.
08 - Brush the tops of each scone with a thin layer of cream. Bake for 18 to 20 minutes until golden brown on top. Cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.
09 - While scones bake, set up a double boiler. Place lemon juice, lemon zest, sugar, eggs, and salt in a heatproof bowl. Whisk until smooth and well combined.
10 - Set the bowl over a saucepan of simmering water, ensuring the bowl does not touch the water. Whisk constantly for 8 to 10 minutes until the mixture thickens enough to coat the back of a spoon and reaches 170°F.
11 - Remove from heat immediately. Add butter pieces one at a time, whisking until each piece melts and the curd becomes smooth and glossy. Let cool to room temperature, then refrigerate until ready to serve.
12 - Split scones in half horizontally. Spread generously with chilled lemon curd and serve immediately. Store leftover scones in an airtight container for up to 2 days.