Drain and rinse the canned pinto beans
Heat oil or butter in a skillet over medium heat
Add chopped onion and cook until soft, if using
Add minced garlic and cook briefly, if using
Add the beans to the skillet
Add a little water, broth, or reserved bean liquid
Mash the beans with a potato masher or fork
Stir and cook until thick and creamy
Add salt to taste
Add black pepper, cumin, chili powder, or other seasonings if desired
Cook a few minutes more, stirring often
Serve warm