Heat the oven to 180C/fan 160C/gas 4.
Heat the olive oil in a large pan or casserole dish, and fry the carrot, onion, celery and peppers for 15 minutes over a medium heat until they are very soft and starting to caramelise.
Add the mince and fry until brown all over.
Add the tomato purée and stir into the mince, then add the chopped tomatoes with half a tin of water and the bay leaf. Bring to the boil and then simmer on a low heat for 30 minutes until the sauce is thick. Season to taste with salt and freshly ground black pepper. Remove the bay leaf!
To make the white sauce, melt the butter on a medium to low heat in a medium saucepan and then add the flour and cook for one minute.
Stirring continually, add the milk gradually until completely incorporated and there are no lumps (I like to use a wooden spurtle).
Turn the heat to low and add 35g parmesan and stir until melted into the sauce.
Stir the spinach though the sauce, and simmer until it wilts. Season with some freshly ground black pepper.
Put half of the tomato sauce in a large baking dish (I used a square Pampered Chef stoneware dish – dimensions: 24cm x 24cm x 5cm deep), and cover with one and half of the fresh lasagne sheets.
Layer the rest of the sauce on top and the finish with the other one and a half fresh lasagne sheets. Pour over the white sauce, and scatter with the remaining 30g of parmesan.
Bake for one hour or until the sauce is bubbling and the top is golden. Cover with foil if it’s getting too dark – I topped ours with foil for the last 15 minutes.