Stir together all dry ingredients
In a glass measuring cup pour in 1/3 cup oil and beaten egg
Fill the glass measuring cup with enough milk to make 1 full cup of liquid ingredients. Depending on the size egg, the amount of milk added will be different every time.
Pour oil, egg, milk, and vanilla into the dry ingredients and stir until fully combined.
Gently fold in blueberries, trying not to break them
Grease or line muffin tin.
Spoon batter into muffin tins until each tin is about 2/3 full.
Place a couple more blueberries on top of each muffin
Make streusel by stirring brown sugar, flour, and butter together.
Sprinkle streusel on top of muffins
Bake at 400 degrees for 20-25 minutes or until golden brown.