• Grease an 8 by 8 square pan with butter. Line all sides with parchment paper. Leave an overhang on at least two sides. Butter the parchment paper. Set aside. Preheat oven to 350 Fahrenheit.
• In a medium saucepan, melt the butter and sweetened condensed milk over medium heat. Stir often until butter has melted. Remove from heat.
• Add the chopped unsweetened chocolate to the melted butter mixture. Stir until chocolate has melted. Set aside and allow to cool slightly.
• In the bowl of an electric mixer or a large mixing bowl using a handheld mixer, beat the sugars, eggs, egg yolk and vanilla extract on medium high for 3 minutes.
• Pour the slightly cooled butter-chocolate mixture into the egg mixture. Stir with a rubber spatula. Sift in the cocoa powder, salt and flour. Stir with a spatula until just combined. Stir in the 1/2 finely chopped banana and chocolate chips. Avoid overmixing.
• Pour mixture into the prepared pan. Bake 25- 30 minutes. Remove from oven. Place pan on a cooling rack and cool completely. 

Banana Pudding

• In a medium heatproof bowl, use a fork to beat the egg yolk. Set bowl next to the stovetop.
• Combine the sugar, cornstarch, flour, and salt  in a medium saucepan. Slowly stir in the milk. Turn the heat on to medium. Stir constantly until the mixture comes to a boil. Cook 2 minutes. Remove from heat. 
• Slowly stir a small amount of the hot milk mixture into the egg yolk to warm the egg yolk. Immediately pour the yolk mixture back into the remaining hot mixture.
• Stir constantly as you cook 2 more minutes. Remove from heat. Stir in butter and vanilla. Stir in the finely chopped overripe banana. Allow to cool for at least 15 minutes. Spread mixutre over the cooled brownies. Top with Nilla wafers (optional).