1/4pound (1 stick)unsalted butter, melted and slightly cooled
1 1/2cupsall-purpose flour
1 1/2teaspoonsbaking soda
1/2cupchopped walnuts, toasted
Preheat oven to 350º. Lightly coat four mini-loaf (2-cup) pans with cooking spray.
Place bananas and sugar in a mixing bowl and beat for 2–3 minutes. Add butter, egg, and vanilla extract, mixing well. Scrape down bowl sides and add flour, cocoa powder, cinnamon, salt, baking soda, and nuts, if using. Mix to combine.
Fill pans about half full with batter. Bake until firm in the center and a toothpick inserted comes out with a bit of crumb on it, 35–40 minutes. (Or use 16 muffin tins and bake 15–18 minutes, or a full-size loaf pan and bake for 1 hour.) Cool completely. To freeze, wrap in plastic and then in foil; freeze up to one month.