01 - Preheat oven to 375°F. Line a 12-cup muffin tin with paper liners or grease thoroughly.
02 - In a large bowl, whisk together flour, sugar, salt, baking powder, and baking soda until well blended.
03 - In a separate bowl, whisk sourdough starter, eggs, melted butter, milk, and vanilla extract until smooth.
04 - Pour wet ingredients into dry ingredients. Gently fold together until just combined—do not overmix.
05 - Fold in blueberries and lemon zest if using, distributing evenly throughout batter.
06 - Divide batter evenly among muffin cups, filling each about three-quarters full.
07 - Bake for 22 to 25 minutes until toothpick inserted in center comes out clean and tops are golden brown.
08 - Let cool in pan for 5 minutes, then transfer to wire rack to cool completely.