I can PM you a recipe from Enzo's breeder for liver treats. Beef liver should work, though I usually make it with chicken liver. Depends on what other problems he may have with food though, since they do contain some grain.I may have to start marking my own treats. I just want to give him something special once a day when I go out and he goes to his crate. He was a big separation anxiety dog when I got him. He seems to have gone backwards recently so I wanted to show him that it wasn't all bad being left alone. A special treat once a day. He seemed so happy to get something different.
I also recommend looking into Ziwi's air dried food - many dogs find it delicious and rewarding to eat as a treat (their treats are literally the same product just in a smaller bag and more expensive).
Alternatives would be freeze-dried raw treats (depending on how you feel about giving raw food). They are usually single ingredient. It's possible to make freeze-dried treats yourself, too, if you feel more comfortable with that, but I believe the process can take up to 2 weeks.