1. Preheat oven to 400°F (200°C) and line a baking sheet with parchment paper.

2. Whisk together flour, sugar, baking powder, salt, and lemon zest in a large bowl.

3. Cut cold butter into the dry ingredients using a pastry cutter until mixture resembles coarse crumbs.

4. Stir sourdough starter, cream, and vanilla extract in a separate bowl, then pour into the dry mixture and stir until just combined.

5. Gently fold in floured blueberries without overmixing to avoid crushing.

6. Turn dough onto a lightly floured surface, pat into a 1-inch-thick circle, and cut into 8 triangles.

7. Chill shaped scones on the baking sheet for 20 minutes to firm up the butter.

8. Brush scones with cream or milk, sprinkle with coarse sugar, and bake for 18–22 minutes until golden and springy to the touch.

9. Whisk together 3/4 cup powdered sugar and 1 tablespoon lemon juice until smooth to make the glaze.

10. Cool scones on a rack for 10 minutes, then drizzle with lemon glaze and serve warm.