Preheat oven to 375 degrees F.
Whisk together oil and sugar until fluffy.
Whisk in sour cream, buttermilk, egg, and vanilla until just combined.
Add in 1 ½ cups flour, salt, and baking powder and stir. Do not overmix.
Toss fresh blueberries with 2 teaspoons flour until all the blueberries are coated.
Add blueberries into mixture and gently fold until incorporated, making sure not to break any of the berries.
Spoon blueberry mixture into a lined or well-greased muffin tin until each tin is 2/3 full.
Prepare brown sugar topping by stirring together brown sugar, flour, and melted butter.
Sprinkle each muffin with a generous coating of brown sugar topping.
Bake in oven for 20 to 25 minutes or until muffins spring back when touched or toothpick comes out clean.