I make liver training treats, Sonny loves them - boil liver (ox seems to be cheapest) for about 10 mins, wash under cold water and rub away all the foamy scummy bits, chop it up into teeny tiny pieces, spread pieces on a baking sheet lined with non-stick paper and pop in the oven at about 160C for 20 mins or until it looks quite dried out and is hard, you may have to move the bits around about half way through, and it may take longer than 20 mins (I don't tend to time it!).