So, don't clean the foie gras too much. You don't want to open the lobes, just remove any bloody parts from the top, and at the bottom you will see a small ball of fat. Pull that off. Also, if you see large veins on the bottom, grab those as well. Season the foie gras with salt and pepper(17g/kilo of salt, 2g/kilo pepper), add 2 g sugar and a few tablespoons of cognac and marinate over night. The next day, heat a large pot of duck fat to 75 degrees C. Add the whole foie gras and cook for 15 minutes keeping the fat around 70 C. Turn the liver and cook about 10 minutes more, or until the center is about 40 C. Foie gras is actually pretty tough to get a good temp reading in, so if you can't 25 minutes total is going to be pretty good. You may even need a little less. You could use a cake tester and then put it on your lip. You wnat the liver to be around body temp, not too much warmer.
OK, so then you take the liver out and place it on a rack at room temp to let it drain. Leave it there for two hours. In the mean time, ladle about a cm of fat into a pretty deep container in which you will store the liver. Put it in the fridge to harden. After two hours, place the liver on cling film and wrap tightly so it becomes either the shape of a nice loaf, or the shape of a cylinder. Either way works. Prick the film wherever you see air gaps in the the liver, then place the foie on top of the congealed fat, and ladle more fat, which should be about room temp or less, over the liver so that it is completely covered. Put the whole thing in the fridge and let it rest for three weeks.
To serve, just remove all of the fat from the plastic wrapped liver, unwrap, slice, top with salt and pepper and have at it.