PUT beans in a pot add water to fill ¾. Add half of the onion, garlic and salt; cover and let them cook for 40 minutes after the press cooker begins to whistle.
HEAT in a big frying pan over medium temperature, while beans are being cooked. Heat.
ADD chorizo and fry lightly until it gets a little browned, for 4 minutes. Meanwhile chop the other onion half, Take the chorizo away from the frying pan and keep.
ADD chopped onion and “chile serrano” in the frying pan, fry for a couple of minutes or until onion gets transparent. Add tomato and let it cook for 5 more minutes, until tomato releases its juice.
POUR water in the frying pan, let it boil and add the bean´s pot, add also chorizo and let it cook for 10 more minutes, everything together. Check season and let it boit over low heat, they must be lightly dense but soupy.
SERVE and decorate with cilantro.