Cut onions and sear with butter.
Meanwhile cut liver into small piece (all the blood will be visible, place / soak in water and swirl and everything nasty will come out - do this multiple times until water runs clear).
Sear liver in olive oil separate from onion pan.
Add liver into onion butter pan and add sour cream couple tablespoons and season (pepper, seasoning salt) and heat through for 5 minutes.
Then cover and steam for 5-10 minutes or so.