First of all you can make this recipe as it is by that I mean combine these ingredients in 1 bowl or you can make 2 separate batches one with chocolate, one with banana and mix to get this colour difference in the cake.
Even if you decide to make this recipe in just 1 bowl or 2 bowls, it's quite simple.
Preheat the oven to 350 degrees, 15 minutes prior to baking.
Sift the flour, cocoa powder in the bowl then add the rest of the dry ingredients and mix.
Add the liquid ingredients, mashed banana and fold.
You can use any kind of bowl to bake it, depending on what you're looking for. If you want a thick layer of cake, use a smaller bowl if you want a think cake like I did, use a bigger one, totally up to you.
Cook the cake until the toothpick comes out clear mine took around 25 minutes, depending on your bowl's size this will change.
Then let it cool down then cut it into sizes, Pour some powdered sugar on top, and you are done.
You can add nuts or white/dark chocolate chips or whatever basically to this recipe and add more sugar if you want a sweeter cake, totally up to you. But I prefer it this way, I'm not a fan of really sweet desserts so -- You can remove the banana and make it a chocolate cake as well but if you're going to do that double the amount of the cocoa powder.