Preheat the oven to 180c.
Heat a saucepan with a little olive oil and cook the onion, carrot and celery until soft, about 5 minutes. Add the herbs, season well before adding the mince and mushrooms. Cook on high for a couple of minutes to brown the meat.
Add the tomato purée, stir well and add the tinned tomatoes. Simmer on a medium heat for about 10 minutes.
Meanwhile make the white sauce by melting the butter in a saucepan and gently whisking in the flour to combine. Slowly add the milk on a medium heat, whisking all the while. Add the nutmeg, bay leaf and pepper. Cook gently for a few minutes until thick and glossy.
Layer a lasagne dish with some pasta sheets, top with a layer of the beef and mushroom mince and pour over a ladleful of white sauce with some grated parmesan. Repeat all the layers until you have used up all the ingredients. The final layer should be white sauce sprinkled with lots of parmesan and cracked black pepper.
Cook in the oven for 25 minutes until golden and bubbling. Leave to cool a little and serve with a green salad.