Do the dough in two halves, replacing 10% of the flour in one half with unsweetened cocoa powder
Let proof
Instead of punching down, roll out flat
Lay one on top of the other and roll up
Leave to finish proofing and then bake
The flavour is detectable but subtle. It still works perfectly as white bread, it just looks fun and has a bit more depth to it if you have it without any strong-tasting toppings