Chocolate-Banana Lunchbox Cake

Preheat oven to 400 degrees F. Lightly oil an 8-by-11 1/2-inch baking dish or coat it with cooking spray.

Whisk together flour, cocoa, baking soda and salt in a large bowl. Whisk together mashed banana, buttermilk, brown sugar, corn syrup, oil and vanilla in a medium bowl. Make a well in the center of the dry ingredients and add the wet ingredients; mix with a wooden spoon or rubber spatula just until the dry ingredients are moistened.

Turn the batter into the prepared baking dish, smoothing the top. Sprinkle chocolate chips and nuts evenly over the top.

Bake until a cake tester inserted in the center comes out clean, about 20 minutes. Let cool in the pan, dust with confectioners' sugar and cut into squares.