Prepare the beans.
Reserve.
Preheat the oven to 325°.
Drain the beans of most of their liquid, but leave them a bit soupy.
Mash half of the beans.
Put all of the beans in an ovenproof serving casserole dish.
Add the white onion, cheeses, jalapeños, jalapeño juice, and cumin.
Mix well.
Bake the bean mixture until hot and bubbling, about 15 minutes.
Drizzle with sour cream and scatter the green onions on top.