Pre-heat the oven to gas mark 4, 350°F (180°C).

Par-boil the lasagne sheets (yes, even the pre-cooked ones) in salted oiled water - about half the time recommended for cooking them, or 3-4 minutes - then drain the sheets and plunge into cold water. Carefully separate them and lay them out to one side hanging from a rack or sides of a pan or colander.

Now make the sauce, which can be done using the all-in-one method. This means placing the milk, butter, flour and bay leaf together in a saucepan, giving it a good seasoning, then, over a medium heat, whisking the whole lot together continually until it comes to simmering point and has thickened. Now turn the heat down to its lowest possible setting and allow the sauce to cook gently for 5 minutes.
After that, stir in 2 oz (50 g) of the Parmesan, then remove it from the heat, discard the bay leaf and place some clingfilm over the surface to prevent a skin from forming. This really works - you only need to put the cling film across the top of the pan too Now you need to deal with the spinach. First of all remove and discard the stalks, then wash the leaves really thoroughly in 2 or 3 changes of cold water and shake them dry. Next, take your largest saucepan, pop the knob of butter in it, then pile the spinach leaves in on top, sprinkling them with a little salt as you go. Now place the pan over a medium heat, put a lid on and cook the spinach for about 2 minutes, turning the leaves over halfway through. After that, the leaves will have collapsed down and become tender.

Next drain the spinach in a colander and, when it's cool enough to handle, squeeze it in your hands to get rid of every last drop of liquid. Then place it on a chopping board and chop it finely. Now put it into a bowl, add the ricotta, then approximately 5 fl oz (150 ml) of the sauce. Give it a good seasoning of salt and pepper and add the grated nutmeg. Then mix everything together really thoroughly and, finally, fold in the crumbled Gorgonzola. Now you need to place a small frying pan over a medium heat, add the pine nuts and dry-fry them for about 1 minute, tossing them around to get them nicely toasted but being careful that they don't burn. Then remove the pan from the heat and assemble the lasagne.

To do this, spread a quarter of the sauce into the bottom of the dish and, on top of that, a third of the spinach mixture, followed by a scattering of toasted pine nuts. Now place sheets of pasta on top of this - you may need to tear some of them in half with your hands to make them fit. Now repeat the whole process, this time adding a third of the grated Mozzarella along with the pine nuts, then the lasagne sheets. Repeat again, finishing with a layer of pasta, the rest of the sauce and the remaining Parmesan and Mozzarella. When you are ready to cook the lasagne, place it on the middle shelf of the pre-heated oven and bake for 50-60 minutes, until the top is golden and bubbling. Then remove it from the oven and let it settle for about 10 minutes before serving.