For the crumb: Position an oven rack in the center of the oven and preheat the oven to 375 degrees F. Lightly spray two standard muffin tins with nonstick spray and line 16 of the tins with muffin liners.
Whisk the melted butter, brown sugar, cinnamon and salt together in a medium bowl.
Add the flour and mix until completely blended and crumbly, then set aside.
For the muffins: Sift together the flour, sugars, baking powder, baking soda and salt in a large bowl. Whisk the dry ingredients to combine, then make a well in the center.
Whisk together the eggs, melted butter, oil, buttermilk and vanilla in a separate bowl. Pour the liquid ingredients into the center of the dry ingredients, then fold together with a spatula just until the dry ingredients are moistened. Don't overmix. Gently fold in the blueberries. Some may break, and that is okay.
Use a 2-ounce scoop or a 1/4 cup measuring cup to portion heaping scoops of batter into each lined muffin cavity. Top each muffin with about 2 tablespoons of crumb, gently pushing the crumb in place.
Bake the muffins until a toothpick inserted in the center of a muffin comes out with a few moist crumbs, about 25 minutes. (You may need to push some of the crumb aside to test the muffins.) Cool for 5 to 10 minutes in the muffin tin, then move to a wire rack to cool. Enjoy warm or at room temperature.
When measuring flour, spoon it into a dry measuring cup and level off excess. (Scooping directly from the bag compacts the flour, resulting in dry baked goods.)