Brown the sausages on all sides over high heat in a dry pan. Place them in the slow cooker.
Add the remaining ingredients, mix and cook on high for 4-5 hours or on low for 8 hours.
An hour before serving, check if the sauce is thick enough. If not, make a paste using 1 tbsp cornflour and a little water, then stir the paste into the pot and let it cook for the last hour, to thicken.