Preheat the oven to 350 F. Line an 8-inch loaf pan with a piece of parchment paper so that the paper hangs over two sides, and spray with non-stick spray.
In a bowl, mash the bananas. Whisk in the sour cream, melted butter, sugars, vanilla and eggs until smooth.
Sift together the flour, baking soda, baking powder, salt and spices. Add the dry ingredients to the wet, and stir just until moistened. If adding chocolate chips or chopped nuts, fold them in now.
Spread the batter into the prepared pan. Bake on the center rack for about 55 minutes, until the top is cracked and a cake tester or sharp knife comes out clean or with moist crumbs clinging to it.
Cool in the pan for 10 minutes, then lift the bread out by the paper and set on a cooling rack to cool for several hours before slicing. Store leftovers in an airtight container for up to three days.
