Cut a pocket in veal breast, or ask your butcher to do it for you. Season pocket with salt and pepper. Preheat oven to 325 degrees. Set aside veal to reach room temperature. In a skillet melt butter over medium-high heat. Add onion and celery and saute until onion is tender and golden.
In a bowl combine bread and eggs; add onion mixture, parsley and 1 cup of the chicken stock. Season with salt and pepper; mix well. Stuffing should be fairly wet; add a little more chicken stock if needed. Using a long spoon, reach deep inside veal pocket to distribute stuffing evenly. Use a trussing needle and string to sew up pocket.
Add the veal roll and brown on all sides. Remove the veal from the pan and reserve. Ditch any excess fat and add a few drops of new oil. Add the onions to the pan, stir to coat with the oil and season with salt. Lower the heat to medium and cook the onions, covered, for 7 to 8 minutes.
Add and stir together the egg, 3 tablespoons of wine, salt, pepper and nutmeg. Add the parsley and bread crumbs, then the sausages, removed from their casings. Mix well. Stuff the pocket of the veal breast with the mixture, gently pressing it into the corners. Sew together the opening with a kitchen needle and string.