Preheat oven to 375F (conventional) and prepare a muffin tray by lining 8 cups with butter (and liners if needed)
Add lemon zest to the sugar in a large bowl and massage with your hands until it looks fluffy
Add the melted butter, oil and vanilla, and whisk for 1 minute
Add the eggs one at a time and mix to combine. Whisk for another minute so the batter is more airy
Sift in the flour, baking powder, baking soda and salt. Fold gently with a rubber spatula until combined. The batter will be quite thick
Add the sour cream and fold until combined. The batter will now be more pourable
Add a spoon of batter into each muffin cup (8 total) - this will prevent the blueberries from sinking to the bottom
Now fold the blueberries in the remaining batter
Divide the batter evenly between the 8 cups
Sprinkle generously with the cinnamon sugar mixture
Bake at 375F for ~25 min or until a toothpick inserted in the center comes out with moist crumbs attached
Enjoy!
