In a large bowl, cream together butter & brown sugar.
Mix in eggs and vanilla. (If adding sour cream, fold in now)
Add mashed bananas. Set aside.
In a separate bowl, whisk or sift together flour, salt, baking soda, baking powder, & cinnamon.
Stir in walnuts if using.
Add the dry mixture to the wet mixture and stir just until combined. Do not overstir.
Pour the mixture into a greased and flour loaf pan and let it sit for about 10-15 minutes before placing into the oven. I don’t know what this does, just something I see my grandmother do all the time.
Place into the oven and cook for 60 minutes or until a toothpick inserted in the center comes out clean. 1 hour always works for me.
When done, remove from oven & butter the top. Let sit in the pan for about 20 minutes before removing it to cool completely.