Next in a large mixing bowl or stand mixer, add in flour, sugar, salt, and baking powder and combine. Then, continue with the oil, egg, and milk and mix well. Lastly fold in the blueberries.
Once done, fill cupcake liners that have been sprayed with non stick cooking spray, up to the top.
Next, combine all of the crumb ingredients in a bowl and mix them together with a fork.
Sprinkle the crumb ingredients evenly over each muffin.
This made 10 regular sized muffins for us; however, original source says 8. It will vary based on size.
Bake 25-30 minutes or until the crumb topping has browned.