Cut the onions in half and then cut each half into about 6 segments.
Heat the olive oil in a casserole over a low to moderate heat. Add the onions and leave to lightly colour, stirring occasionally to make sure they dont stick.
Add the garlic , fennel seeds and bay leaves to the onions. Push the mixture to the side of the pan then add the sausages and lightly brown all over.
Once browned, mix with the onions then add the passata and 125 ml water. Add 1 tbsp of the grain mustard and simmer for a few minutes then season.
Add the beans, check seasoning and simmer gently for 20-25 minutes until the sausages are cooked and the liquid reduced. Stir in another tablespoon of the grain mustard and simmer for a couple of minutes more before serving.