Preheat oven to 325°F. Line a 24-cup mini muffin tin with liners or spray well.
Mix crumbs, 3 tbsp sugar, and melted butter; press about 1 tsp into each cup. Chill 5 minutes.
Beat cream cheese until smooth, then add sour cream, ½ cup sugar, egg, and vanilla until combined.
Fold in blueberries gently. Spoon filling over crusts, leaving room for streusel.
Make streusel: cut butter into flour, brown sugar, and salt until chunky. Sprinkle over cheesecakes.
Bake 15–18 minutes until centers slightly jiggly. Cool on rack 30 minutes, then chill at least 1 hour.