Tip all the ingredients into a slow cooker.
Pour in enough water to come halfway up the pot. You don;t need to cover all the ingredients.
Switch on to high and cook for 3-4 hours, or low and cook for 6-8 hours.
If you would like to thicken the gravy, in a glass or cup, stir a little cold water into the cornflour to make a smooth paste. Pour this into the slow cooker and stir well.
Pop the lid back on and leave for 5 minutes to thicken.
Stir again, and serve.