Preheat oven to 400°F (200°C) and line or grease 8 muffin cups.

In a large bowl, whisk flour, sugar, baking powder, and salt.

In a separate measuring cup, combine oil, egg, and milk until smooth.

Pour wet ingredients into dry ingredients and mix until just combined.

Gently fold in blueberries.

In a small bowl, mix sugar, flour, butter, and cinnamon until crumbly.

Fill muffin cups to the top with batter.

Sprinkle crumb topping generously over each muffin.

Bake Blueberry Muffins for 20–25 minutes until golden and a toothpick comes out clean.

Let cool slightly before serving.