Crumble Topping:
Mix ½ cup sugar, 1/3 cup flour, ¼ cup butter, and 1½ teaspoons cinnamon. Refrigerate mixture until ready to use.
Muffins:
Preheat the oven to 375°F. Line a 12-cup muffin tin with paper liners. Spray the pan and the liners with non-stick cooking spray.
In a medium bowl, whisk together the flour, sugar, baking powder and salt.
In a separate bowl, combine oil, milk and egg. Whisk until well incorporated. Gradually add the flour mixture. Add the blueberries to the batter and fold gently with a rubber spatula until evenly distributed. Do not overmix.
Scoop the batter into the prepared muffin tin. Sprinkle the crumble topping evenly on top of the muffins. Bake for about 25-30 minutes, until lightly golden. Let the muffins cool in the pan for about 10 minutes. Run a knife around the edge of each muffin to loosen from the pan, (the blueberries get a little sticky), transfer the muffins to a cooling rack to cool completely. Enjoy!
