I'm eating it raw, liver is a lot more tasty raw than cooked. Get calf liver if you're worried about accumulated toxines. If it's been frozen for 2 weeks no need to worry about parasites, I prefer it fresh though.

Liver is extremely nutrient dense, and experts that I trust believe that the benefits far outweigh any risks due to the fact that it is an organ that cleanses the body. Natural and free roaming animal sources are naturally superior. It should look fresh and vibrant, and be cooked promptly upon purchasing. I feel terrific when I eat liver, and that is why I do so.