01 - Preheat oven to 400°F. Line baking sheet with parchment paper.
02 - In large bowl, whisk together flour, sugar, baking powder, baking soda, salt, and lemon zest.
03 - Add cold butter to flour mixture. Using pastry blender or fingertips, cut butter until mixture resembles coarse crumbs.
04 - In small bowl, whisk buttermilk, egg, and vanilla extract. Pour over flour mixture and stir gently until just combined.
05 - Fold in blueberries carefully, taking care not to crush them.
06 - Turn dough onto lightly floured surface. Gently knead once or twice, then pat into 1-inch thick circle. Cut into 8 wedges.
07 - Transfer wedges to prepared baking sheet. Brush tops with cream or milk and sprinkle with coarse sugar if desired.
08 - Bake for 18-20 minutes until golden brown. Transfer to wire rack to cool.
09 - In heatproof bowl, whisk lemon juice, zest, sugar, and eggs.
10 - Set bowl over saucepan of simmering water (double boiler). Whisk continuously until thickened and coats back of spoon, about 8-10 minutes.
11 - Remove from heat and whisk in butter until smooth. Transfer to jar and cool completely.
12 - Serve scones warm or at room temperature with generous dollop of lemon curd.