Heat oven to 375°F. Line muffin tins with baking cups or grease well with cooking spray.
In a medium bowl, mix together the flour, baking powder and salt. Set aside.
In a large bowl, mix together the butter, oil, and sugar with a fork until smooth. Add the eggs, vanilla, and milk and mix well until combined.
Add the flour mixture into the liquid mixture and stir just until most of the streaks of flour are incorporated. Fold in the blueberries, being careful not to smash them. If using frozen blueberries, do not defrost before adding them to the batter.
Fill each baking cup ¾ full, then add a few extra blueberries on the top of each muffin, if desired. Mix the flour, sugar, salt, and melted butter together in a medium bowl using a fork for the crumb topping, then divide evenly among the muffins, sprinkling about 1 tablespoon of the top of each muffin before baking.
Bake for 22-25 minutes, until done. Cool for 5-10 minutes before transferring to a wire rack to cool completely.