1. Marinate the bison cubes in wine overnight (8 hours).
2. Drain and place the cubes in a slow cooker along with the tomatoes, veal stock, salt & pepper.
3. Heat the duck fat in a large frying pan. Brown the onions and add in the leek and then mushrooms.
4. Transfer the vegetables to the slow cooker and cook for 8 hours at low heat.

For a thick sauce:

1. Remove the meat and vegetables from the slow cooker with a slotted spoon and transfer the juice to a saucepan.
2. Prepare a mixture of equal parts flour and soft butter and whisk vigorously. Add 1/3 cup (75 ml) of this mixture for every 4 cups (1 L) of juice to be
3. Bring to sauce a boil, stirring regularly. When thickened, return to slow cooker.
4. Return the meat and vegetables to the slow cooker and cook for another 15 minutes.