Peel and finely chop the garlic. Peel and roughly chop the onions.
Gently heat the butter in a large deep sided frying pan. Add the onions and garlic and sauté for about twenty minutes until softened and almost translucent.
Meanwhile soak the dried porcini in about 100 ml of warm water and thickly slice the fresh mushrooms.
When the onions are ready add the sliced mushrooms and partially cover with a lid, then cook until coloured and softened.
Add the porcini and their soaking water, the parsley, 4 or 5 tbsps of parmesan and the cream.
Season with salt and ground black pepper and cook, stirring, until the cream has thickened and reduced.
Spread a thin layer of béchamel sauce over the bottom of a large baking dish. Cover with a single layer of lasagne sheets then a third of the mushroom mixture. Repeat two more times and finish with a layer of lasagne.
Spread the pesto over the pasta and then spread over the remaining béchamel sauce. Sprinkle with the remaining parmesan.
Bake at 180 C ( 160 C fan) for about 50 minutes or until bubbling and golden.