Preheat the oven to to 350°F.Spray or grease a 4 1/2×8 1/2-inch loaf pan very well.

Make the batter:Mash the bananas in a mixing bowl using a fork. Whisk in the melted butter, milk, egg, and vanilla. Mix in the sugar.In another mixing bowl, using the hand mixer (or a whisk), beat peanut butter until smooth. Beat this into the banana mixture. Scrape the bowl down and beat in the baking soda, salt, and cinnamon (if using).

Fold in the flour and chocolate chips:Fold in the flour until completely combined, followed by the chocolate chips.

Bake the loaf:Spread the batter in the prepared pan and bake at 350°F on the center rack of the oven for 55 to 60 minutes, or until the bread is deeply golden and a toothpick inserted in the center comes out clean.

Cool the loaf:Remove the bread from the oven and place on a rack to cool completely before turning out.

Enjoy!Store the leftover bread wrapped well in plastic at room temperature for 3 days. Leftovers are great toasted lightly in a pan with butter.