01 - Preheat oven to 400°F. Line a baking sheet with parchment paper.
02 - In a large bowl, whisk together flour, sugar, baking powder, baking soda, and salt until well combined.
03 - Add cold, cubed butter to the flour mixture. Use a pastry cutter or fork to cut in butter until mixture resembles coarse crumbs.
04 - In a separate bowl, whisk egg, sour cream, lemon juice, lemon zest, and vanilla extract until smooth and fully incorporated.
05 - Pour wet mixture into dry ingredients. Stir with a spatula until just combined. Be careful not to overmix as this will result in tough scones.
06 - Gently fold blueberries into the dough until evenly distributed.
07 - Transfer dough to a lightly floured surface. Pat into a 1-inch thick circle. Cut into 8 equal wedges and place on prepared baking sheet, leaving space between each.
08 - Bake for 16-18 minutes or until tops are golden brown and a toothpick inserted in the center comes out clean. Cool on baking sheet for 5 minutes before transferring to a wire rack.
09 - Whisk together powdered sugar, vanilla extract, and 2 tablespoons milk. Add additional milk as needed to reach drizzling consistency.
10 - Drizzle glaze over cooled scones. Allow glaze to set for 5-10 minutes before serving.