Preheat oven to 400°F.
Wash and pat your blueberries dry. If using frozen, let them mostly thaw first.
Use that extra 1 Tbsp of flour to coat the blueberries by tossing them in it. This helps prevent them from sinking through the muffin batter and ending up on the bottom of the muffins.
In a bowl, combine the flour, baking powder, baking soda, and salt.
In your mixer's bowl, combine the sugars and lemon zest.
Add the butter and 1 Tbsp of the vegetable oil to the sugar mixture, and cream together until fluffy. Then, mix in the remaining oil.
Add the eggs one at a time, making sure each is well-mixed before adding the next.
In another bowl, mix together the buttermilk, sour cream, and lemon juice.
Add ⅓ of the flour mix to the mixture and fold with a rubber spatula until almost combined.
Add half of the buttermilk mixture and fold until almost combined.
Add half of the remaining flour and fold. Then, the remaining buttermilk mixture. Then, the remaining flour mixture. Fold until almost fully combined each time.
Add the blueberries and carefully fold them in. This will finish mixing the batter and incorporate the berries. It will look fluffed up, but be a fairly thick batter.
Line your muffin tins with muffin cups. Fill each cup about half way with batter.
Generously sprinkle the crumble topping on top of the muffin cups.
Bake for 12-15 minutes, or until a toothpick inserted into them comes out clean.
Let mostly cool, and enjoy!