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, baking soda, salt, and lemon zest until well combined.
03 - Add the cold butter and cut it into the flour mixture using a pastry blender or your fingertips until the mixture resembles coarse crumbs with some pea-sized pieces remaining.
04 - In a small bowl, whisk together buttermilk, egg, and vanilla extract until blended.
05 - Pour the wet mixture over the flour mixture. Stir gently with a spatula or wooden spoon until just combined. Do not overmix.
06 - Fold in the fresh blueberries carefully, taking care not to crush them.
07 - Turn the dough out onto a lightly floured surface. Gently knead once or twice, then pat into an 8-inch circle about 1-inch thick. Cut into 8 equal wedges using a sharp knife or bench scraper.
08 - Transfer wedges to the prepared baking sheet, spacing them 2 inches apart. Brush tops with cream or milk and sprinkle with coarse sugar if desired. Bake for 18-20 minutes until golden brown and cooked through. Transfer to a wire rack to cool slightly.
09 - In a heatproof bowl, whisk together lemon juice, lemon zest, sugar, and eggs until smooth and well combined.
10 - Set the bowl over a saucepan of simmering water, creating a double boiler. Whisk continuously for 8-10 minutes until the curd thickens enough to coat the back of a spoon.
11 - Remove from heat and immediately whisk in the butter until smooth and melted. Transfer to a clean jar and let cool completely. Refrigerate until ready to serve.
12 - Serve scones warm or at room temperature with a generous dollop of chilled lemon curd.