Step 1

Preheat the oven to 350°F. Line a 9 by 5-inch metal loaf pan*** with parchment paper, leaving an overhang. Spray with nonstick cooking spray.

Step 2

In a large bowl, whisk together the flour, cocoa powder, sugars, baking soda, and salt.

Step 3

In a medium bowl, stir together the bananas, sour cream or yogurt, eggs, butter, oil, and vanilla. Gently fold the wet ingredients into the dry ingredients until just barely combined. Gently fold in the chocolate chips, being very careful not to overmix. Spread batter into the prepared pan.

Step 4

Bake until slightly domed and the internal temperature registers at least 200°F with an instant read thermometer, about 1 hour to 1 hour 10 minutes. Cool in the pan on a cooling rack for 15 minutes before using the parchment overhang to remove the loaf from the pan to finish cooling completely. Bread will collapse slightly as it cools.

Step 5

Once the bread has cooled, place the chocolate chips in a double boiler set over simmering water or place in a microwave-safe bowl and microwave in 20-second bursts, stirring between bursts, until melted. Drizzle over the top of the cooled loaf (coating will be thick). Let set before serving, serve same day for best appearance.

Step 6

Wrap leftovers in plastic wrap or foil and store at room temperature for up to 3 days. The banana flavor will intensify the longer it sits, and the chocolate coating will harden as the loaf sits and may bloom (slightly discolor). If you prefer, microwave slices before serving to soften.