Preheat oven to 350 degrees.
In a stand mixer with the paddle attachment mix the bananas and brown sugar until the bananas are mashed and the sugar is dissolved.
Add the apple sauce, vanilla, and egg. Mix together.
In a separate bowl mix the flour, cocoa powder, baking soda, and salt. Add the dry ingredients to the wet ingredients and mix until well incorporated.
Fold in the semi-sweet chocolate chips. Pour batter into a greased 8x8 baking dish. Sprinkle the top with the mini chocolate chips. This will become the frosting.
Bake for 50 minutes, testing at 35 minutes with a toothpick.
Serve while warm.