Bring 2/3 of the pumpkin cubes to the boil together with the onion, garlic, stock and cream. Cook for 5 - 10 minutes. Take the pot off the stove and puree well. Now add the remaining pumpkin cubes and the herbs, bring to the boil again and season with salt, pepper and nutmeg.
In a greased casserole dish, layer the pumpkin sauce with the lasagne plates alternately and always spread a few mozzarella cubes on top of the sauce. For the top layer, first cover the lasagne plates with sauce, spread the creme fraiche on top and spread the rest of the mozzarella on top.