Heat the oil in a large pan and fry the onion, carrot and celery for 8-10 minutes, until golden and tender. Season, add the mince and cook for a further 5-6 minutes until browned all over.
Stir in the tomato purée and chopped tomatoes. Rinse the tomato cartons out with a good splash of water and add this to the pan. Bring to the boil then simmer for 10-12 minutes until the sauce has thickened slightly.
Meanwhile, mix 2 tbsp of the milk with the cornflour into a paste. Pour the remaining milk into a pan, season and bring to a gentle simmer. Stir in the cornflour paste and soft cheese. Cook for 2-3 minutes, stirring frequently, until thickened, then stir in the cheese – reserving a little for the top of the lasagne.
To assemble, spread a third of the meat sauce over the base of an 18cm baking dish. Top with 3 of the lasagne sheets, then a third of the white sauce. Continue with the rest of the ingredients, before sprinkling over the reserved cheese.
Bake in a preheated oven at 200°C/fan 180°C/gas mark 6 for 35-40 minutes, until golden and bubbling.
*When compared to our standard lasagne recipe, this recipe has more than 30% less calories.