1. In a small bowl, mix streusel flour, brown sugar, and salt. Cut in the cold butter until the mixture becomes coarse crumbs. Chill while you prepare the batter.

2. Preheat oven to 375°F (190°C). Line a 12-cup muffin tin with liners.

3. In a large bowl, whisk together flour, sugar, baking powder, baking soda, salt, and lemon zest.

4. In a separate bowl, whisk eggs, buttermilk, melted butter, and vanilla until well combined.

5. Add the wet ingredients into the dry mix and stir gently until just combined.

6. Carefully fold in blueberries using a rubber spatula.

7. Divide batter evenly among muffin cups, filling 3/4 full.

8. Sprinkle streusel topping generously over each muffin.

9. Bake for 18–22 minutes, until a toothpick comes out clean. Cool in tin 5 minutes, then transfer to a wire rack.

10. Whisk powdered sugar and lemon juice into a glaze and drizzle over cooled muffins before serving.