Preheat oven to 350°F and prepare 2 standard muffin pans with non-stick muffin liners or grease and flour pans.
Add sourdough starter, butter, eggs, sugar, milk, and vanilla to a large mixing bowl and whisk until smooth.
Add flour, baking powder, baking soda, cinnamon, and salt to the mixing bowl and whisk for 1 minute until the batter is smooth, it will be very thick.
Fold in fresh blueberries.
Make the crumb topping. Add flour and sugar to a small mixing bowl, and cut in butter until the mixture is a course crumb.
Spoon muffin batter into pan, filling each space 3/4 way with batter. Top each muffin with 2 teaspoons of crumb topping.
Bake in a preheated oven at 350°F for 18 minutes or until a toothpick comes out of the center of the muffins clean.
Make the glaze. Whisk powdered sugar, cream, and vanilla until smooth. Set aside.
Allow muffins to cool on a wire rack for 10 minutes, drizzle glaze over the top, and serve or store.