Mix together flour, baking powder, sugar salt.
Add in melted butter, sour cream, egg, milk, vanilla.
Stir until just combined.
Add in blueberries and stir to incorporate. Do not over stir.
Spray muffin tin with non stick spray and fill four muffin tins to the top.
Combine streusel topping ingredients until they look like wet sand.
Add streusel topping to top of muffin.
Preheat oven to 425 degrees F and cook muffins for FIVE minutes.
Reduce temperature (leaving muffins in the oven) to 350 degrees F for 25 minutes or until a toothpick comes out clean.
