In a microwave safe dish, melt your butter and set it aside to cool. Be careful not to add it to the batter while it is hot or it could scramble your egg.
Next, add the dry ingredients (flour, sugar, baking soda, cinnamon, and salt) to a large mixing bowl. Stir well with a large spoon or spatula.
Add in your wet ingredients (vanilla extract, eggs, mashed bananas, butter, and sour cream). Mix well with a hand mixer until well combined and no longer lumpy.
Pour into a well greased 9 x 5 inch loaf pan.
Bake for 50 to 55 minutes at 350 degrees or until a toothpick comes out clean from the middle.