01 - Preheat the 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 the all-purpose flour, granulated sugar, salt, baking powder, and baking soda until evenly distributed.
03 - In a separate bowl, whisk the sourdough starter, eggs, melted butter, whole milk, and vanilla extract until the mixture is smooth and well combined.
04 - Pour the wet ingredients into the dry ingredients. Using a spatula, gently fold together until just combined. Be careful not to overmix—small lumps are acceptable and will result in tender muffins.
05 - Gently fold in the blueberries and lemon zest (if using) until evenly distributed throughout the batter.
06 - Divide the batter evenly among the prepared muffin cups, filling each about three-quarters full. An ice cream scoop works well for portioning.
07 - Bake for 22 to 25 minutes, or until a toothpick inserted into the center of a muffin comes out clean and the tops are golden brown.
08 - Allow the muffins to cool in the pan for 5 minutes before transferring to a wire rack to cool completely.