To a food processor add 1/3 cup flour, 1 1/2 Tbsp granulated sugar and diced butter. Pulse several seconds just until butter is distributed and until it somewhat comes together in tiny crumbles, it should still be fluffy. Set aside.
For the Blueberry Muffins:
Preheat oven to 400 degrees F. In a mixing bowl whisk together flour, baking powder, baking soda and salt for 30 seconds, set aside.
In a separate large mixing bowl, using a wire hand whisk, mix together 1 cup granulated sugar, canola or vegetable oil, buttermilk, sour cream and eggs until well blended, about 30 seconds. Using a rubber spatula, fold in flour mixture just until combine (batter should be slightly lumpy. Don't over-mix, key to fluffy muffins).
Gently fold in blueberries. Divide mixture evenly among 12 paper lined muffin cups. Fluff crumb topping with a fork and sprinkle each muffin evenly with 1 Tbsp crumb topping mixture. Sprinkle tops with raw sugar.
Bake muffins in preheated oven 18 - 22 minutes, until lightly golden and toothpick inserted in the center of muffin comes out clean. Allow to cool several minutes in muffin pan before removing to wire rack to cool. Best served day baked.
*Use the scoop and level method to measure flour.
**In a pinch, make your own buttermilk by mixing 1/4 cup milk with 3/4 tsp vinegar or lemon juice, let rest 5 minutes before using.