Preheat the oven to 375 degrees F (190 degrees C). Line 10 muffin cups with paper liners.
Combine blueberries and 2 teaspoons flour and toss to coat.
Combine 1 cup flour, baking soda, cinnamon, and salt in a bowl. Whisk sourdough starter, sugar, egg, melted butter, and vanilla extract together in a second bowl. Whisk briskly until no streaks appear. Mix flour mixture with sourdough mixture, and stir well. The batter will be quite thick. Fold blueberries into the batter.
Spoon batter evenly into the prepared muffin cups.
Combine sugar, flour, butter, and cinnamon for the topping in a bowl and mix with a fork until crumbly. Sprinkle topping over the muffins.
Bake in the preheated oven until tops spring back when lightly pressed and a toothpick comes out clean, 20 to 22 minutes. Cool in the pan for 10 minutes. Transfer to a wire rack to cool completely.