Most people cook beef liver in combination with onions and bacon. One easy method is to lightly flour the liver and brown in a small amount of olive oil in a skillet, and set aside. Add onions slices and butter to fill the pan and cook until lightly caramelized. In a lightly greased baking pan, alternate layers of the onion butter mixture and the browned liver pieces, starting and ending with the onions. Cover with foil and bake at 350 degrees for about one hour, or until the liver is thoroughly cooked and tender.