Season the venison with salt and pepper. Heat a large, heavy based frying pan over medium-high heat and add a little oil. Sear the venison on all sides – allow about 1 ½ to 2 minutes for each side –, then remove from pan and wrap lightly in foil to rest.
Add the onion, garlic and mushrooms to the pan, along with half the butter. Cook over a medium heat for about 3-5 minutes until golden and softened. Add the Mayan Chilli Chocolate spice, bay leaf and thyme and cook for a further 2 minutes. Deglaze the pan with the port and red wine and allow to reduce by at least half before adding the stock. Reduce by half again.
Strain the sauce into a clean saucepan and whisk through the dark chocolate and remaining butter to form a smooth, glossy sauce. Season to taste.
