Preheat oven to 375°F. Line a muffin tin with paper liners
In a medium bowl, whisk flour, baking powder, baking soda, salt
In a large bowl, cream together butter and sugar until light and fluffy. About 2 minutes
Add eggs, mixing well until fluffy, add vanilla
Mix in sour cream and milk until combined
Gently fold in the dry ingredients until just combined, do not overmix
Toss fresh blueberries with 1 tbsp flour, then fold them into the batter
Let the batter rest for 10 minutes for fluffier muffins
In the meantime, make the crumble by adding butter, sugar and flour into a bowl, with your hands gently combine until it creates a crumble
Divide the batter evenly into the muffin tin, sprinkle the crumble on top, top with more blueberries (optional)
Bake for 22-25 minutes or until a toothpick in the center comes out clean
Let it cool for 5 minutes, then transfer to a wire rack and let it cool completely before slicing. About 20 minutes
