Make a single cut down the length of the first loin, cutting to within ½ inch of the bottom. Making two more cuts, to the right and left of the center cut. Gently spread the loin out and cover with a piece of plastic wrap.
Pound the cut loin carefully, to about ½ inch thickness. Do the same with the other loin. Now lay them side to side, overlapping by about 1 inch.
Preparing the stuffing. In a large skillet over medium heat, sauté the onions and celery in the butter until soft. Then add the remaining ingredients. Stir until the bread cubes are covered and all the moisture has been absorbed.
Preheat the oven to 325 degree. Spread the stuffing mixture on the overlapping loins and roll the loins, jelly-roll style. Tie the roll tightly as for any rolled roast. Put the roast in a shallow roasting pan and cook, uncovered, 45 minutes for rare, 55 minutes for medium.
Serve with baked potatoes, and fresh, buttered asparagus.