Prepare pans and oven. Position a rack in the center of the oven and preheat to 400oF (205℃). Brush the insides of the muffin pan with softened butter and then brush the top of the pan. Or use liners for easier removal, like I did). You can also use cooking spray. In a small bowl, prepare the streusel by using your fingers until combined and crumbly. Set aside.
Make the streusel. In a small bowl, stir together the flour, cinnamon, and sugars. Stir int the melted butter, until combined and crumbly. Set aside.
Combine dry ingredients. Whisk the flour, brown sugar, baking powder, salt, and orange zest together in another bowl.
Toss blueberries in flour. In a small bowl, stir blueberries with 1 tablespoon of the flour mixture. Set aside.
Combine wet ingredients. Whisk the oil, milk, orange juice, and eggs together in a medium bowl.
Combine wet and dry ingredients. Add to the liquids, and stir with a spatula or wooden spoon just until combined; do not over mix. Fold in the blueberries.
Scoop muffins. Using a 2 1/2-inch diameter ice-cream scoop, portion the batter, rounded side up, into the prepared muffins cups. You can fill the muffins almost to the top, leaving just a little room for the streusel. Generously, sprinkle the tops with the streusel.
Bake the muffins. Bake for 10 minutes. Reduce the oven temperature to 375°F degrees and continue baking until the tops of the muffins are golden brown and wire cake tester inserted into the center of a muffin comes out clean about 15 minutes more. If using frozen berries, allow a few extra minutes. Cool in the pan for 10 minutes. Remove the muffins from the pan and cool completely.