For the bechamel sauce:
- Melt butter in a saucepan over low heat; add the flour. Stir vigorously with a whisk so that no lumps are formed. Pour in the milk and cook over medium heat until it thickens enough to coat the back of a spoon. Stir occasionally with a whisk to avoid lumps. Season with salt, pepper and nutmeg. Remove sauce from heat and set aside.
For the lasagne:
- Preheat oven to 200 C / Gas 6.
- Use a ladle to pour a layer of bechamel sauce over the bottom of a 20x30cm baking dish. Add the pesto to the remaining bechamel and stir to mix.
- Lay 3 lasagne sheets side by side and cover with 1/4 of bechamel sauce mixed with pesto. Add 1/3 of mozzarella and sprinkle with 1/4 of Parmesan cheese. Repeat the same layering finishing with bechamel sauce and an even layer of grated Parmesan cheese on top.
- Bake for 30 to 40 minutes or until the pasta is fully cooked and golden brown. To achieve a nice golden colour, you can cook it under the grill for the last 5 minutes.
- Remove from oven, cover with foil and let stand for 15 minutes before slicing and serving.
If you use thin fresh lasagne, you won't need to cook the sheets before baking. If they are thick - dip each sheet in salted boiling water for 1 minute, drain and pass quickly under the cold tap to stop the cooking process. Lay them on a tea towel and pat dry before using.
Parmesan cheese is not truly vegetarian, as it can sometimes contain animal rennet. To make this dish 100% vegetarian, find a suitable vegetarian substitute made without animal rennet. In supermarkets look for the 'parmesan style hard cheeses' which are suitable for vegetarians.