Preheat your oven to 350º F (180º C) and butter a 9x5 inch loaf pan, lining the bottom with parchment paper.

In a medium bowl, mash ripe bananas until smooth.

In a separate bowl, whisk together the flour, baking soda, and salt.

In a large bowl, mix melted butter, neutral oil, granulated sugar, light brown sugar, and vanilla until combined. Add eggs one at a time, mixing thoroughly.

Stir in mashed bananas and Greek yogurt or sour cream until just combined.

Gently fold the dry ingredient mixture into the wet mixture.

Melt chocolate until smooth, then combine with 1 cup of the banana batter.

Alternate scooping dollops of the banana and chocolate batters into the prepared loaf pan and swirl together gently.

Bake for 55 to 65 minutes, tenting with foil after 30 minutes. Test for doneness with a toothpick.

Let the bread cool in the pan for 15 minutes before transferring to a wire rack to cool completely.