Cupcakes: Preheat oven to 350 degrees F. Line 2 muffin tins with cupcake liners.
Combine flour, salt and baking soda in a medium size bowl.
In a larger bowl, whisk egg and add brown sugar, mixing until smooth. Stir in vanilla extract. Add greek yogurt and melted butter and mix. Stir in dry ingredients, then add mashed bananas and milk, mixing until batter comes together. Stir in the chocolate chips. Set aside.
Brownies: Place butter in a large bowl, add cocoa and stir until well blended.
Beat eggs with a mixer. Add sugar and vanilla, beat well. Stir in the butter mixture.
Add flour and salt. Mix until just combined. Stir in chocolate chips.
Take about 1/8 of a cup of the banana batter and place it in the bottom of all the cupcake liners. You want the cupcake liners to be about 1/4 of the way full. Then take a tablespoon of the brownie batter and place it in the middle of each cupcake (try and stay in the center of the cupcake). Then add just enough of the banana batter to cover the brownie batter (you want your cupcake liner to be about 3/4 of the way full).
Bake for 15-18 minutes. Let cool completely.
For the Meringue: In a large pot, bring about 2 inches of water to a simmer.
In a large, heat-proof bowl, whisk together egg whites, sugar, corn syrup and salt. The mixture will be grainy, because of the sugar.
Place bowl over simmering water and whisk as it heats. The sugar will dissolve after about 5 minutes. Keep and eye on the mixture, it shouldn’t get warm enough to cook the eggs.
Transfer the egg white and sugar mixture to the bowl of an electric stand mixer. With a whisk attachment, beat the egg whites, on high, until stiff peaks form (about 5 minutes). The mixture will be fluffy and glossy and look like melted marshmallows. It’ll be sticky too. Beat in the vanilla extract last. Cover, and set aside until ready to frost cupcakes.
Place a big dollop of frosting on each cupcake (or you can get all fancy and pipe it on) and smooth it out with a knife.
Turn on oven broiler.
Place 12 cupcakes on a baking sheet. Place cupcakes under the broiler for about 1 minute. Don’t even close the broiler door. Keep an eye on them as they toast. You may need to remove the cupcakes and rotate the pan to ensure that they cook evenly. Once toasted, remove cupcakes, and toast the remaining 12.
If desired drizzle with chocolate sauce.