Mix all ingredients for the marinade in sequence and season to taste. Soak the steaks and let them cool in a closed container for 2 days before eating.
Remove the steaks and let them drain.
Bring the rest of the marinade to the boil in a saucepan and pour in the wine. Add the cocoa powder and reduce for about 45 minutes. Thicken with a sauce thickener and allow to cool.
The quantities given are sufficient for 4 beef steaks of 600 g each.