Stuffing: In a food processor blend the veal and the fat. With the motor running, add the eggs, 1 at a time and combine well. With the motor still running, add the heavy cream in a stream Transfer the mixture to a large bowl and add the remaining ingredients. Chill, covered, for at least 30 minutes. On a double thickness of cheesecloth arrange the turkey breast skin side down with a long side facing you. Sprinkle it with the thyme and salt and pepper to taste. Smooth half the stuffing over the turkey breast, leaving a 1-inch border. Cover the stuffing with a layer of the ham, using slightly more than half. Smooth the remaining stuffing over the ham and arrange the remaining ham slices, with the short ends facing you, on the turkey breast. Center the turkey breast fillets lengthwise on the ham and fold the ham over them. Beginning with the long side of the breast nearest you, roll it carefully away from you into a cylinder shape. Tie the ends securely with string. Preheat the oven to 350 degrees. In a roasting pan heat the butter and oil over moderate heat until hot and in it brown the turkey, patted dry. Add the stock and cheesecloth bag and bring the mixture to a boil. Braise the ballottine, covered tightly with foil, in the middle of the oven, basting occasionally, for 11/2 hours, or until the juices run clear when the breast is pricked with a skewer. The ballottine can be made 1 day ahead up to this point and kept refrigerated, covered, in the cooking liquid. To reheat, bring to a boil over moderately high heat, baste, and heat, covered, in a preheated 350 degree oven, basting frequently for 1 hour. Transfer the ballottine to a rack to cool. Unwrap it. Skim the braising liquid and strain it into a saucepan. In a small bowl combine the arrowroot, Madeira, and cream. Bring the strained liquid to a boil and stir in the arrowroot mixture. Cook the mixture over moderately high heat until it is thickened slightly. Keep the sauce warm, covered with a buttered round of waxed paper. Transfer the ballottine to a carving board and slice half of it into 1/2-inch slices. Transfer the slices and remaining ballottine to a platter and serve warm with the sauce.
TO BONE A TURKEY
With a sharp knife and your fingers, cut and pull the wishbone from the turkey breast. Turn skin side down and, starting at the severed backbone and working toward the ridge of the breastbone, cut the breast meat of half the breast away from the carcass, keeping the knife angled against the bones and pulling the meat away as it is cut. Turn so the other side of the backbone is facing you and cut away the meat in the same manner. With the knife angled against the breastbone, sever the meat completely and discard the carcass. Lay the breast skin side down. Remove the fillets, trim off any tendons and sinews and reserve. Cut the breast to a uniform 1-inch thickness by slicing horizontally into the thicker sections. Use some of the trimmings to patch any areas where there is little or no meat. Cover the breast with moistened waxed paper and with a mallet or the flat side of a cleaver pound to flatten slightly.