I would love to turn this into a chocolate sponge cake. Any thoughts?

If I were going to do this, I'd focus on what about thisAlice Medrich recipe I want to retain and then search for one that combined it (say, the brown butter or the tiger nut flour) with chocolate in a recipe that's already been made.
I'm not sure about the proportions of adding chocolate or cocoa to the recipe as written, so I might just make the recipe as written and add a chocolate icing instead of the dusting of sugar as the final garnish.