Sauté the onion rings in a skillet with lard (or oil) and a pinch of salt over medium-low heat until soft.
Add cooked beans and a splash of their cooking liquid to the pan and allow to simmer.
Mash the beans and onion together using a masher until mostly mashed and the onions have disappeared.
Adjust the consistency with more bean-cooking liquid as needed.
Taste and adjust seasonings as desired.
