Prepare a muffin tin by greasing or filling with paper liners. Preheat your oven to 400°F (200°C).
In a large bowl, combine all dry ingredients and mix well with a fork or whisk (flour, sugar, baking powder and salt).
In a measuring cup, add the ⅓ cup vegetable oil, the egg, and then fill with milk up to the 1 cup mark. Stir wet ingredients together.
Add your wet ingredients into your dry ingredients and mix until combined. Gently fold in the blueberries. Your batter will be quite thick.
In a small bowl mix all ingredients for the crumb topping. During this step, it is most efficient to use your hands to really mash the butter and fully incorporate everything. This may take a few minutes of mixing and mashing.
Fill your muffin tins almost to the top with the muffin batter, and layer the top with the crumb mixture. You should have enough batter and crumb topping for 12 muffins.
Bake in the preheated oven for 20 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Cool muffins on a rack for 20 minutes before enjoying.