Line your muffin pan with cupcake liners or spray with non-stick cooking spray. In a large mixing bowl, beat or whisk together sourdough starter, eggs, the melted butter, sugar, vanilla extract, and milk.
Take 1 tablespoon out of the ½ cup of flour and mix it with the blueberries. Sift together flour, salt, and baking powder in a small bowl and set aside. Mix dry ingredients into the wet ingredients and stir gently, just until combined. Do not overmix.
Gently fold the blueberries into the muffin batter—divide the batter between the muffin cups in the prepared pan.
Mix flour, baking powder, sugar, and brown sugar. Use a pastry blender or a fork to cut the butter into the flour mixture to form small crumbs. Add heavy cream and stir to combine into larger clumps.
Sprinkle the streusel topping over the tops of the muffins. Add a few blueberries to the top of the streusel if you’d like. Bake for 10 to 12 minutes at 325°F, bake until a toothpick inserted in the center of the muffins comes out; clean until the tops are golden brown.
Cool muffins in the pan for about 5 minutes and then move them to a cooling rack to finish cooling.
Plate, serve, and enjoy!