Preheat your oven to 400 degrees. Line a 12 cup muffin tin with paper liners and set aside.
Whisk together the flour, sugar, salt and baking powder. Mix in the oil, egg, buttermilk, and vanilla until combined. Fold in your blueberries. Divide the batter evenly between your prepared liners. I like to use a cookie scoop to keep things even.
In a small bowl whisk together the brown sugar, flour, butter, and cinnamon. Sprinkle onto the tops of your muffin batter.
Bake for 20-23 minutes or until a toothpick comes out clean.