Melt 4 tablespoons butter in large heavy frying pan or casserole.
Add the onions, carrots, celery, and parsley, and sauté lightly until onions are golden.
Add the ground beef and veal, salt and black pepper, and cook, stirring, on moderate heat for 15 minutes, or until meat is browned.
Add mushrooms and cook, stirring, for 5 minutes.
Add tomato pulp and broth, and cook for 30 minutes, uncovered, stirring occasionally.
Remove from heat and set aside.
Cut the uncooked egg pasta into about 4-inch squares.
Plunge 6 to 8 pasta squares into boiling water salted water.(If you use commercial lasagne, follow the instructions for time of cooking on the box, and cook them all at the same time. But, as soon as you remove from water, toss with butter, so that they will not stick together, and you'll easily make the layers.)
As soon as pasta squares rise to the top, let them cook for about 2 or 3 minutes.
Remove from water one at a time with a slotted spoon and place, unfolded, on thick towels.
Dry well and line bottom of a well-buttered deep rectangular or square pan or casserole.
(Use the remaining cooked pasta squares to make a second layer.)
Cover the pasta with a layer of the meat-mushroom sauce.
Sprinkle with 2 tablespoons shredded prosciutto and 1 tablespoon Parmesan cheese, then dot with 1 tablespoon butter.
Repeat process of boiling only enough pasta squares at a time to make one or two layers (it always depends on the pan or casserole you use), draining, adding to casserole, and topping with sauce, shredded prosciutto, Parmesan cheese, and butter.
Top with final layer of pasta, sprinkle with Parmesan cheese, dot with remaining butter, and place in oven for 15 to 20 minutes at 350F, or until top is golden and edges of pasta crisp and curly.
Remove and serve with a bowl of remaining Parmesan cheese.
Note: This recipe for lasagne can be prepared well ahead of time, but in that case the baking time in the oven must be increased in order to heat thoroughly the lasagne.
* tomato pulp: 1 to 1 1/2 lbs ripe tomatoes. Drop in boiling water for about 10 seconds.
Remove with a slotted spoon, peel, seed and chop.
Source: Northern Italian Cooking Francesco Ghedini Hawthorn Books, Inc.