Pick over the beans, then rinse. Place in a large bowl and cover with plenty of filtered water. Soak overnight, adding additional water if necessary. Rinse and drain well.

Place oven rack in the lower-middle position. Preheat oven to 300F/135C/gas mark 1.5.

Pick the leaves from about 20 cilantro sprigs and set aside in the fridge. Tie up the rest of the cilantro plus all the bare stems with kitchen twine.

If using, cook bacon in a Dutch oven or heavy oven-safe pot until crispy. Remove to a paper-towel-lined plate.

Peel and finely chop the onion. Peel and finely mince the garlic.

Sauté the onion and garlic in the bacon fat or 2 tbsp coconut oil over medium-high heat until golden brown, about 10 minutes.

Remove from heat, stir in tequila. Return to medium heat (careful, it may flame up) and cook until most of the liquid is gone, about 10 minutes.

Increase heat to high, stir in 3-1/2 cups filtered water, bay leaves, salt (if using), beans, and cilantro bundle. Bring to a boil.

Cover with the lid (or heavy-duty foil with a tight seal) and place in the oven for 60 minutes, or until beans are tender.

Transfer pot from the oven to the stove on medium heat. Fish out bay leaves and cilantro bundle with tongs. Stir in beer. Bring to a boil, then turn down to a "vigorous simmer" for 30 minutes, stirring frequently, until beans are completely tender and liquid is thick. (This is where you would add the can of tomato paste if desired.)

Serve topped with reserved crumbled bacon (or coconut bacon), minced reserved cilantro, lime wedges, and Cotija cheese if you eat dairy.