Preheat oven to 350 degrees. Line a 9x13 baking dish with parchment.

In the bowl of your stand mixer, cream together the butter and sugar until light and fluffy. Add 1 whole egg and the yolks of 2 eggs. Set aside the egg whites for the topping.

In a small bowl combine the flour, baking powder, and salt. Add to the butter mixture and beat until fully incorporated. Spread the batter in the prepared baking dish. It will be thick, so just use your fingers to smoosh it all around the pan.

In a microwave safe bowl, heat the hot fudge and peanut butter until they are a pourable consistency. Pour over the batter in the baking dish and spread to cover.

Beat the 2 egg whites until stiff peaks form. Fold in the brown sugar gently. Spread this over the hot fudge and peanut butter.

Bake for 30 minutes or until the top is golden brown and the bottom crust is cooked through, but not crunchy.

Cool and then cut into bars and serve.