Preheat your oven to 375°F (190°C). Line a muffin tin with paper liners or grease it lightly with butter or cooking spray.

In a large mixing bowl, combine the flour, sugar, baking powder, and salt. Mix well to ensure there are no lumps.

In another bowl, whisk together the vegetable oil, egg, milk, and vanilla extract until smooth. Pour the wet ingredients into the dry ingredients and stir gently until just combined. Be careful not to overmix; a few lumps are okay.

Gently fold in the fresh blueberries, ensuring they are evenly distributed throughout the batter.

In a small bowl, combine the flour, sugar, and cinnamon for the crumble topping. Add the cold butter cubes and use your fingers or a fork to mix until the mixture resembles coarse crumbs.

Divide the muffin batter evenly among the prepared muffin cups, filling each about ⅔ full. Sprinkle a generous amount of the crumble topping over each muffin.

Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted into the center of a muffin comes out clean. Allow the muffins to cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.