First make the bolognese sauce. Heat the oil in a saucepan and cook the prosciutto and onion until softened then add the carrot and garlic. Stir and cook for 2 minutes. Add the mince, breaking it up with a wooden spoon and browning. Add the pasta sauce, then put 1 cup of water in jar, replace the lid and shake to dissolve remaining sauce and then add to saucepan. Add herbs. Simmer until meat is cooked.
To make the bechamel sauce, melt butter over medium heat and stir in flour. Continue stirring until smooth and golden (approx. 5 minutes). Whisk in milk until thickened then reduce heat to low and simmer for 15 minutes. Add nutmeg, salt and pepper.
Spread small amount of bolognese sauce on the bottom of a large baking dish and cover with lasagne sheets. Spread 1/3 of the sauce over sheets, then spread 1/4 of bechamel sauce over. Sprinkle with a little parmesan then repeat building layers and ending with bechamel. Sprinkle remaining parmesan on top and cover with foil you've sprayed with oil (underneath so it doesn't stick.)
Bake 45 minutes. Remove foil then bake an additional 15 minutes or until heated through.