Preheat oven to 325°F. Spray a 9x5" baking loaf with nonstick spray. Line with parchment paper if desired.
In a large bowl, cream butter and sugar. Then mix in eggs, vanilla and sour cream.
Next add in the flour, baking soda, and salt. Stir just until combined. Fold in bananas.
Pour into 2 (8x4) loaf pans and bake for 55 minutes, or until a toothpick comes clean and lightly browned. If using a 9x5 pan you can put the batter into one pan, but you will need to cook 10-15 minutes longer. If it's browning too fast, cover lightly with foil.
Once the bread is slightly cooled, remove from the pan and place on a cooling rack. Store leftovers in a zip top bag or wrap in foil.
To make muffins: Pour batter into muffin tins. This recipe makes 24 regular-sized muffins. Bake for about 20 to 25 minutes, until lightly golden and toothpick comes out clean. To make small loaves: This mixture will fill 4 small loaf pans. Bake for 35 to 45 minutes, until lightly golden brown and toothpick comes out clean.