1. Preheat oven to 350°F and grease 9×13-inch pan. Line bottom with parchment paper, leaving overhang on two sides.

2. In large bowl, mash bananas until mostly smooth. Stir in ½ cup melted butter, then add ¾ cup sugar, 2 eggs, and 1 teaspoon vanilla. Whisk for 30 seconds until fluffy.

3. Sprinkle baking soda and ½ teaspoon salt over wet mixture and stir. Add 1½ cups flour and gently fold just until barely combined.

4. Fold ½ cup chocolate chips into banana batter with 2-3 gentle strokes. Reserve a few chips for topping.

5. In medium bowl, whisk together ¼ cup melted butter, ½ cup sugar, 1 egg, and ½ teaspoon vanilla. Add cocoa powder, ¼ cup flour, and ¼ teaspoon salt. Stir just until combined.

6. Pour banana bread batter into prepared pan and spread evenly. Dollop spoonfuls of brownie batter in 8-10 spots scattered across the surface.

7. Use a butter knife to swirl brownie batter through banana batter in figure-eight or zigzag pattern. Make 8-10 passes—don’t over-swirl.

8. Sprinkle remaining ¼ cup chocolate chips over top, pressing slightly so they adhere.

9. Bake for 30-35 minutes, until edges are set and toothpick comes out with a few moist crumbs. Brownie areas may look slightly underdone.

10. Cool in pan for 30 minutes, then lift out using parchment overhang. Cool completely (about 1 hour) before cutting into 24 bars.