1) Finely chop the chorizo into small dice. In a heavy-baased saucepan, add the olive oil and chorizo. Put the saucepan over low heat and slowly bring the heat up to medium. Fry the chorizo for a few minutes to infuse the olive oil.
2) Using a slotted spoon remove about 50g of chorizo, for garnish, and set aside.
3) To the remaining chorizo in the pan, 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 flavours to come together, about 10 minutes. Season with salt and pepper, to taste.
4) 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.
5) Transfer to large bowl and serve.