Put the beans in a saucepan and barely cover them with stock. Bring to a boil and simmer for 5 – 10 minutes until the stock has been reduced to about 25ml.
Mash the beans with a potato masher and then mix in the mustard and parsley. Leave to one side in a bowl.
Heat a tablespoon of olive oil in a pan and soften the onion over a low heat. Add the garlic and cook for another 1-2minutes.
Add the onion and garlic to the bowl of mashed beans and mix well.