Preheat your oven to 475 degrees. Wash your fresh blueberries and gently dry them with a paper towel. Spread them on evenly on a plate and pop them into the freezer until you are finished making the batter. Freezing the fresh blueberries for a bit prevents them from sinking and from bleeding in the batter.
Add all of the dry ingredients to one bowl mix to combine and set aside.
In another bowl, add the sugar, eggs, vanilla, vegetable oil and melted butter. Using a hand whisk (not an electric whisk.see notes), whisk for 1.5 minutes.
Add the buttermilk to the wet ingredients and whisk for 30 seconds.
Pour the wet ingredients into the dry ingredients and mix until just combined. Be careful not to over-mix or you’ll have chewy muffins!
Take the the cold blueberries out of the freezer and fold them into the batter.
Add all the streusel ingredients into a bowl.
With a fork mix all the ingredients together until it clumps together.
Divide the batter into a muffin lined tin.
Top each with streusel then very gently press down so it sticks.
Bake at 475 for 7 minutes then reduce the temperature up 350 and bake for another 25-30 minutes or until a toothpick inserted into the center of a muffin comes out clean.