In a large saucepan or flameproof casserole dish, heat the oil and brown the sausages with the onions for 10 mins until golden. Add the garlic and spice mix with 75ml water to prevent them from burning, and cook for 2 mins until fragrant. Add the dates and tomatoes, mix well, then spread out onto 2 plates to cool before pouring into a freezer bag and freezing for up to 3 months.
To cook from frozen, put the stew into a large saucepan or flameproof casserole dish with all but 2 tbsp of the stock. Cover with a lid and gently heat to defrost for 25 mins, stirring occasionally.
Once the stew is fully defrosted, mix the cornflour with the reserved stock and pour into the pan. Bring to the boil and simmer, uncovered, for 5 mins until thickened and piping hot. Serve with mashed potato.