Marbled Banana Bread

Heat oven to 350°F. Butter a 9×5-inch loaf pan, or coat it with nonstick baking spray.

Melt butter in the bottom of a large bowl in the microwave. Mash the bananas right into it until mostly smooth.

Whisk in brown sugar, egg, vanilla, baking soda, and salt until thoroughly combined. Add 1 cup of the flour, stirring just until it disappears.

Pour half of the batter into a second bowl. Into one bowl, stir the remaining 1/4 cup of flour and ground cinnamon. Into the other bowl, stir in the cocoa powder and chocolate chips.

Dollop batters in large alternating spoonfuls into the bottom of the prepared loaf pan, attempting to "checkerboard" the rest in.

Use a butter knife or small offset spatula to make a few figure-8s through the batters, marbling them together.

Bake for 55 to 65 minutes, until a tester or toothpick inserted into the center comes out batter-free.

Cool in the pan for 10 minutes, then run a knife around the edge and invert it onto a cooling rack.

Serve warm or at room temperature.

Do ahead: The banana bread will keep for up to 4 days at room temperature. Wrap in foil.