Preheat oven to 400 F
Thoroughly grease muffin tins or line with muffin liners
Combine flour, sugar, salt, baking powder, vegetable oil, vanilla, egg, and milk.
Gently fold in dewberries.
Fill muffin cups 3/4 of the way full
For crumble topping:
Mix together sugar, flour, butter and cinnamon using a hand or stand mixer until a nice crumble forms. Sprinkle on top of muffin batter and bake for 22-24 minutes, or until golden brown.