Preheat oven to 400°F (200°C). Grease muffin cups or line with muffin liners.
Combine flour, sugar, salt, and baking powder. Place vegetable oil into a 1-cup measuring cup; add the egg and enough milk to fill the cup. Mix this with flour mixture.
Fold in blueberries. Fill muffin cups right to the top, and sprinkle with crumb topping mixture.
Bake for 20 to 25 minutes in the preheated oven, or until done.