To make the crumb topping, in a bowl, combine the sugar, flour, butter and cinnamon and mix with a pastry blender or 2 forks until a coarse consistency is reached. This recipe makes enough crumb topping for another batch or 2 of muffins, which you will want to make soon. 

To make the muffins, preheat the oven to 350°F. Grease the wells of a 12-cup muffin pan. 

In a bowl, stir together the flour, sugar, salt and baking powder. Pour the vegetable oil into a 1-cup liquid measuring cup and add the egg. Fill with enough milk to total 1 cup liquid. Stir the milk mixture into the flour mixture, then carefully fold in the blueberries. Divide the batter among the prepared muffin cups and sprinkle with the crumb topping. 

Bake until the muffins are golden and a toothpick inserted into the center comes out clean, 20 to 25 minutes.