01 - Preheat oven to 375°F. Line a 12-cup muffin tin with paper liners or grease thoroughly with butter or cooking spray.
02 - In a large mixing bowl, whisk together all-purpose flour, granulated sugar, salt, baking powder, and baking soda until evenly distributed.
03 - In a separate bowl, whisk sourdough starter, eggs, melted butter, whole milk, and vanilla extract until completely smooth and emulsified.
04 - Pour wet mixture into dry ingredients. Gently fold together with a spatula just until combined—batter should remain slightly lumpy. Avoid overmixing to prevent tough muffins.
05 - Gently fold blueberries and lemon zest into batter until evenly distributed. If using frozen berries, add directly from freezer without thawing.
06 - Divide batter evenly among prepared muffin cups, filling each approximately 3/4 full. Use an ice cream scoop for consistent portioning.
07 - Bake at 375°F for 22 to 25 minutes until tops are golden brown and a wooden toothpick inserted into center comes out clean.
08 - Let muffins cool in pan for 5 minutes, then carefully transfer to a wire cooling rack. Allow to cool completely before serving.