Heat oil in the bottom of a medium-sized heavy pot or Dutch oven (if finishing on the stove), in the pot of a pressure-cooker, or in a large skillet (if finishing in a slow-cooker). Once warm, add onion and cook for 5 minutes, until translucent. Add any fresh peppers and cook for 3 more minutes. Add garlic, chili powder, cumin, oregano, and salt and cook for 2 minutes, until browned and deeply fragrant. Add beer and scrape up any bits stuck to the pot. Boil until reduced by half, or, if you are worried about alcohol content, until it has all but disappeared.

If finishing on the stove: Add tomato sauce, dried beans, any dried or rehydrated-and-pureed chilles and the smaller amount of water. Bring mixture to a full boil and boil for one minute, then reduce heat to a very low, gentle simmer, place lid on your pot, and cook for 2 ½ to 3 hours, until the beans are tender, stirring occasionally. Add the last ½ cup water if mixture seems to be getting dry.

If finishing in a slow-cooker: Scrape onion, spice, and beer mixture into a slow-cooker. Add tomato sauce, dried beans, any dried and rehydrated-and-pureed chilles and the smaller amount of water. Cook on high for 6 to 7 hours, until beans are tender. Add extra water if necessary.

If finishing in a pressure-cooker: Follow the directions from your pressure-cooker manufacturer; estimated time to prepare the dish in this way is 20 to 22 minutes on high.

Serve as is or with lime wedges, sour cream, diced white onion, cilantro, corn or flour tortillas, or tortilla chips or rice.