Instructions

• Preheat oven to 350°F (175°C). Line two muffin tins with cupcake liners and set aside.
• Make the cupcake dry mix: in a medium bowl whisk together 1 1/3 cups all-purpose flour, 1 1/4 teaspoon baking soda, and 1/4 teaspoon salt. Set aside.
• Make the cupcake wet mix: in a large bowl whisk 1 large egg until combined. Add 3/4 cup loosely packed brown sugar and whisk until smooth. Stir in 1 teaspoon vanilla extract, 1/4 cup Greek yogurt, and 1/2 cup butter, melted. Mix until combined.
• Combine cupcake batter: add the dry mix to the wet mix and stir until mostly incorporated. Stir in 3 cups mashed ripe bananas and 1/3 cup milk until the batter comes together. Fold in 1 cup chocolate chips. Set cupcake batter aside.
• Make the brownie batter: in a large bowl stir 1/2 cup butter, melted (1 stick) together with 4 tablespoons cocoa powder until smooth.
• In a separate bowl, beat 2 eggs (with a mixer or whisk) until combined. Add 1/2 cup granulated sugar and 1/2 teaspoon vanilla extract and beat until well combined. Stir the egg mixture into the butter–cocoa mixture.
• Add 3/4 cup flour and 1/4 teaspoon salt to the brownie mixture and mix until just combined. Fold in 1/2 cup chocolate chips. Do not overmix.
• Portion cupcake batter into liners: spoon about 1/8 cup of the banana cupcake batter into the bottom of each lined muffin cup so each liner is roughly 1/4 full.
• Add the brownie center: using a tablespoon, place approximately 1 tablespoon of brownie batter in the center of each cupcake, trying to keep it centered and not touching the sides.
• Top with remaining cupcake batter: add enough banana batter over each brownie center so each liner is about 3/4 full.
• Bake the cupcakes on the middle rack at 350°F for 15–18 minutes, or until a toothpick inserted into the banana portion (not the brownie center) comes out with a few moist crumbs. Remove from oven.
• Let cupcakes cool in the pans for 5 minutes, then transfer to a wire rack and let cool completely before frosting.
• Prepare the meringue (toasted marshmallow frosting): place a pot with about 2 inches of water over medium heat and bring to a gentle simmer.
• In a large heat-proof bowl whisk together 4 large egg whites, 1 1/2 cups granulated sugar, 1/2 cup light corn syrup, and a large pinch of salt until grainy.
• Place the bowl over the simmering water (bowl should not touch the water) and whisk continuously until the sugar is dissolved and the mixture is warm to the touch, about 4–6 minutes. Do not allow the mixture to get so hot that the eggs start cooking.
• Transfer the warmed egg-white mixture to the bowl of a stand mixer fitted with the whisk attachment. Beat on high until the meringue is glossy, fluffy, and holds stiff peaks, about 4–6 minutes. Beat in 2 teaspoons pure vanilla extract at the end.
• Frost the cooled cupcakes: using a spoon, spatula, or piping bag, place a generous dollop of meringue on each cupcake and shape as desired.
• Toast the meringue under the broiler in batches: turn the oven broiler on high and place up to 12 cupcakes on a baking sheet. Put the sheet under the broiler with the oven door slightly ajar and watch constantly; toast for about 30 seconds to 1 minute, rotating the pan as needed so the tops brown evenly. Remove when nicely browned. Repeat with remaining cupcakes.
• If desired, drizzle cupcakes with homemade hot fudge or store-bought hot fudge before serving.
• Serve immediately after toasting for best texture.