Put the slices of veal between sheets of plastic wrap and pound with a flat mallet without breaking the tissues. Set aside. Combine the prosciutto and pork in a mixing bowl. Melt 1 tablespoon of the butter in a small skillet and cook the onion, stirring, until it is wilted. Add this to the mixing bowl. Add the garlic, bread crumbs, nutmeg, pepper, lemon rind, egg and cheese. Blend well. Lay out the pieces of veal on a flat surface. Sprinkle with salt and pepper. Spoon an equal portion of the filling on each slice. Wrap the meat around the filling, folding and tucking the ends in envelope fashion. Tie each roll neatly in 2 places with string. Sprinkle with salt and pepper. Dredge the rolls all over in flour and shake off any excess. Select a heavy skillet large enough to hold the rolls in 1layer without crowding them. Melt the remaining 3 tablespoons of butter and, when it is quite hot but not browned, add the veal rolls. Cook, turning occasionally, until the are nicely browned all over, 3 or 4 minutes. Reduce the heat and continue cooking over moderately low heat for about 15 minutes. Add the wine and stir to dissolve the brown particles that cling to the bottom and sides of the pan. Add the chicken broth. Bring to the boil and let cook over high heat for about 5 minutes. Remove the strings and serve the veal rolls with the sauce spooned over.