Preheat the oven to 350°F. Line two regular-size muffin tins with paper baking cups.
In a large bowl, whisk together the flour, salt, baking soda, baking powder, and cinnamon. In a separate bowl, whisk the oil and sugars together until combined. Stir in the vanilla, bananas, and sour cream. Add in the eggs, one by one, stirring after each addition.
Stir the dry ingredients into the banana mixture until combined. Stir in the walnuts.
Fill each paper cup 3/4 of the way full. Bake for 20 minutes or until golden brown and a toothpick inserted into the middle of a muffin comes out clean. (If you use the large muffin cups, they’ll cook for around 25 minutes. You can also bake this as a loaf of bread; allow about 50 to 60 minutes.)
Let cool on a cooling rack for 10 minutes before serving. If you want to freeze them, cool completely and place in a Zip-loc freezer bag.