Heat the ghee in a large saucepan over medium heat. Add the chorizo or bacon (if using), stirring regularly until browned and caramelised, about 3–4 minutes.
Add the leek and garlic and cook, stirring occasionally, for 10 minutes, until the vegetables are soft and translucent.
Add the paprika, cumin and fennel seeds and stir through for 1 minute, until fragrant. Deglaze the pan with a splash of the bone broth.
Add the beans, passata, rest of the bone broth and molasses. Stir well and bring to the boil, then reduce heat to low to reach a slow simmer.
Cover with a lid and let the mixture bubble away for 1 hour, or until thick and delicious, stirring occasionally and adding a splash of water if the mixture gets too thick and is burning on the bottom.
Season to taste with salt and pepper and garnish with chopped parsley to serve.