Preheat your oven to 350 degrees. Lightly grease or butter the sides of a 9×13 inch glass baking dish. This will help the cake release easily once baked. The smell of the oven warming up already gets you excited, doesn’t it?
In a medium bowl, whisk together the all-purpose flour, whole wheat pastry flour, baking powder, salt, and cocoa. This dry mixture will give structure to your cake, so be sure to incorporate it well.
In a large bowl, whisk together the eggs and sugar until smooth. This should take a couple of minutes. You want the mixture to be light and fluffy, which helps in creating a wonderful texture.
Add in the milk and melted coconut oil, whisking until everything is well combined. The warmth of the oil will help to melt the sugar and create a silky batter. Stir in the mashed bananas and vanilla until mixed.
Slowly stir in the dry ingredients, mixing until just combined. You want to avoid over-mixing, as this will lead to a dense cake. A few lumps are perfectly fine!
Now it’s time to fold in the chocolate chips. They will melt beautifully while baking, creating delightful pockets of chocolate throughout the cake.
In a small bowl, blend the butter with the brown sugar. Spread this mixture evenly in the greased baking dish. It will create a lovely caramel layer at the bottom of your cake.
Arrange the sliced banana in the dish over the butter and sugar mixture. This not only adds flavor but also gives a beautiful presentation once the cake is flipped.
Spoon dollops of the peanut butter into the dish, filling in the gaps with the cake batter. This will make each bite creamy and delicious!
Bake for about 45 to 55 minutes or until a toothpick inserted into the center comes out clean. The edges should be slightly golden, and the aroma will be heavenly!
Once baked, let the cake cool for 10 minutes. This allows it to set. Then, loosen the edges with a knife and invert onto a platter. This is the moment of truth—don’t be shy, it’s going to look stunning!
While the cake cools, make the warm peanut butter caramel sauce. Combine the remaining butter, brown sugar, peanut butter, and vanilla in a microwave-safe bowl. Melt it in the microwave for about 30 seconds at a time, stirring after each interval, for a total of 1 minute.
Once everything is melted and mixed, pour the warm sauce over the cake just before serving. You might want to keep a napkin handy; it’s going to get messy in the best way possible!