Finely chop the chorizo into small dice. In a heavy-bottomed pot add olive oil and chorizo. Put the pot over low heat and slowly bring the heat up to medium. Fry the chorizo for a few minutes to infuse the olive oil. Using a slotted spoon remove about 1/4 cup of chorizo, for garnish, and set aside. To the remaining chorizo in the pot add the onion and garlic and fry until both are cooked, about 2 minutes. Add the beans with their liquid and stock and simmer to allow the flavors to come together about 10 minutes. Season with salt and pepper, to taste. Use a potato masher to mash the beans into a coarse puree. Alternatively, you could let the beans cool for about 5 minutes and carefully puree in a food processor until smooth. Transfer to a serving bowl.