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 blended.
03 - Add cold, cubed butter to the flour mixture. Use a pastry cutter or fork to cut in butter until mixture resembles coarse crumbs with some pea-sized pieces remaining.
04 - In a separate bowl, whisk egg, sour cream, lemon juice, lemon zest, and vanilla extract until smooth and fully combined.
05 - Pour wet mixture into dry ingredients. Stir gently with a spatula or wooden spoon until just combined. Do not overmix as this will result in tough scones.
06 - Gently fold in fresh blueberries, taking care not to crush them.
07 - Transfer dough to a lightly floured surface. Pat into a 1-inch thick circle. Cut into 8 equal wedges and arrange on prepared baking sheet, leaving space between each scone.
08 - Bake for 16-18 minutes or until tops are golden brown and a toothpick inserted in the center comes out clean. Cool on a wire rack for at least 10 minutes before glazing.
09 - Whisk powdered sugar, vanilla extract, and 2 tablespoons milk until smooth. Add additional milk, 1 teaspoon at a time, until reaching desired drizzling consistency.
10 - Drizzle vanilla glaze over cooled scones. Allow glaze to set for 5 minutes before serving. Best served warm or at room temperature.