Pre-heat your oven to 400.
In a large mixing bowl, mix together the butter & sugar for 2 minutes.
Once fully combined, add in 1 egg at a time & mix again.
Then add vanilla, sour cream, and milk. Mix again. Set aside.
In a smaller bowl, whisk together flour, baking powder, & salt.
Gently fold the dry batter into the wet batter.
Gently fold in the blueberries – overmixing can cause bleeding
Scoop into a lined muffin pan.
Combine all of the ingredients for the streuesel
topping & generously coat each muffin
Bake according to muffin size:
Mini muffins: 15-18 minutes
Standard muffins: 24-26 minutes
Large muffins: 32-35 minutes