Funny you ask, just yesterday I made some for my son to take away with him, along with some steaks of course.
You put some venison bones under the grill and roast well until slightly burned,perhaps even more than slightly !
Place in a pot with onions,carrots, clove of garlic pressed slightly, add some water, salt and pepper.
Pop in a bay leaf and boil down for 4 or 5 hours then add about half a bottle of red wine and a wine glass of port.
Reduce this again, taste and season as required.
Pour through a sieve leaving only the liquid.
Finally add a piece of dark chocolate.
.You can store by freezing in an ice cube mould. That way you can take out as much as you need.