1. Cook the spinach, following the instructions on the packet. Put the lasagne in a bowl and pour boiling water over to cover. Leave to soak for two minutes.
2. Meanwhile, put the ricotta, mascarpone, egg yolk and Parmesan in a food processor and mix. Add the drained spinach and process again. Season with salt, pepper and nutmeg.
3. Preheat the oven to 180C/350F/Gas
4. Put a spoonful of the mixture on a drained sheet of lasagne. Fold over to enclose the filling and place in a greased ovenproof dish, folded side down. Repeat until all the lasagne is used up, then pour the sauce over and sprinkle with mozzarella. Bake for 30 minutes until golden.