Cook the potatoes in a large pan of boiling water for 10 minutes. Add the cauliflower and cook for 8-10 minutes or until everything is soft. Drain and set aside in the covered pan.
Meanwhile, mist a large pan with cooking spray and put over a medium heat. Add the onion, carrots, celery and garlic, and cook for 6-8 minutes until soft. Add the beef and cook for 4-5 minutes, or until it is brown and cooked through.
Preheat the oven to 180°C/Fan 160°C/ Gas 4. Add the tomato purée, tomatoes and bay leaf to the mince mixture and season well. Crumble in the stock cube, then stir in 300ml water and bring to the boil.
Reduce the heat and simmer for 15 minutes until the sauce has reduced and thickened. Add 100g of the peas, stir through and cook for a further minute. Remove and discard the bay leaf.
Mash the potatoes and cauliflower with the low-fat spread and season to taste. Pour the mince mixture into 6 individual ovenproof pie dishes and top with the mash, using a fork to spread it evenly. Bake for 20-25 minutes or until golden.
About 5 minutes before the end of cooking time, cook the remaining peas in a pan of water for 3 minutes, then serve with the cottage pie. The cottage pie can be frozen in an airtight container for up to 3 months.