Preheat your oven to 400°F with a rack in the lower middle. Using a standard 12-well muffin pan, place a muffin liner in each well, or if you don't have muffin liners, grease the inside of the muffin pan wells with vegetable oil or butter.
Melt the butter in a covered medium-sized microwavable bowl. Mine took a minute on high heat. Allow cooling slightly.
Mix the sour cream, vanilla, oil, and milk right into the warmed butter.
In a large mixing bowl mix together the flour, sugar, baking soda, baking powder, and salt then form a well in the middle and add the sour cream mixture and eggs. Mix well to combine. Note: The mixture will be thick.
Fold in the blueberries.
Divide the batter equally among the muffin cups. You'll need to fill them very high to use all of the batter in 12 muffins, which is fine. They won't spill. If you still have too much batter, start filling another pan.
Bake until muffin tops are golden and just firm, 15 to 20 minutes, rotating muffin tin from front to back halfway through baking time. Cool muffins in the muffin pan for 5 minutes, then transfer to wire rack and cool another 5 minutes before serving.
To usefrozen blueberries in blueberry muffins, just toss them in some flour to coat and help absorb any extra moisture. No need to defrost!
For mini muffins, bake 9-11 minutes, but keep an eye on them while they bake as mini muffins bake fast.
This batter should be thick, not fluid. If the batter is too runny, add flour, a tablespoon at a time until it becomes scoopable.
If the batter looks dry or too thick add extra milk, a tablespoon at a time until the proper consistency is reached.
Don't overmix over mixing will result in a dense muffin instead of light and fluffy.
For domed tops: Nearly fill the muffin pan papers. It takes a lot of batter to build a nice dome.