Add flour, baking powder, cinnamon, and salt into a bowl and stir, then set aside.
2 1/2 cups all-purpose flour, 1 tbsp baking powder, 1/2 tsp cinnamon, 1/4 tsp salt
In another large bowl, add the white sugar, oil, eggs, and vanilla. Whisk well to combine, then whisk in the milk.
2/3 cups oil, 1 cup white sugar, 2 large eggs, 1 tbsp vanilla, 3/4 cups milk
Combine the dry and wet ingredients together gently with a spatula just until a muffin batter begins to form. Don't over-mix!
Toss the blueberries in 1 tsp of flour, then add them into the batter and mix a few times until no flour streaks appear. (Try not to add any extra flour that may remain in the bottom of the blueberry bowl if possible)
1 1/2 cups blueberries
Scoop and divide evenly between the liners. Fill the tulip liners halfway (and regular liners all the way), then sprinkle a handful of streusel on top.
Bake for 25-35 minutes or until a toothpick inserted in the middle comes out clean. Begin checking around 20 minutes.
Allow to cool, then enjoy! These coffee cake muffins are so delicious.