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. Cut in with a pastry cutter or fork until mixture resembles coarse crumbs with some pea-sized butter pieces remaining.
04 - In a separate bowl, whisk egg, sour cream, lemon juice, lemon zest, and vanilla extract until smooth and fully incorporated.
05 - Add wet mixture to dry ingredients. Stir gently with a spatula until just combined, being careful not to overmix as this will result in tough scones.
06 - Gently fold in fresh blueberries until evenly distributed throughout the dough.
07 - Transfer dough to a lightly floured surface. Pat into a 1-inch thick circle, approximately 7 inches in diameter. Cut into 8 equal wedges and place on prepared baking sheet, spacing 2 inches apart.
08 - Bake for 16-18 minutes or until golden brown on top and a toothpick inserted in the center comes out clean. Cool on baking sheet for 5 minutes, then transfer to a wire rack.
09 - While scones cool, whisk powdered sugar and vanilla extract together. Add milk gradually, 1 tablespoon at a time, until mixture reaches a smooth, drizzling consistency.
10 - Drizzle vanilla glaze generously over cooled scones. Allow glaze to set for 5-10 minutes before serving. Best served warm or at room temperature.