Cook Rabe in boiling water 3 min; plunge into an ice bath for 1 min. Drain well. Wrap Rabe in paper towels; squeeze dry. Chop Rabe into 1 1/2 in. pieces. Place in bowl with 1 Tablespoon Oil, 1/4 tsp. Salt, Pepper and Garlic, stir well.
Preheat oven to 325 degrees
Cut into Pork Loin lengthwise from right to left, 3/4 in. from bottom, keeping knife parallel with cutting board. Do not cut through the other side. Continue slicing lengthwise from right to left, unrolling loin as you slice, to form a 2/4 in. thick rectangle. Season with remaining 3/4 tsp. salt. Arrange Prosciutto in layers to cover inside of loin. Spread Rabe mixture on top, leaving a 1 in. border. Roll Pork up left to right. Tie with twine in knots at 2″ intervals.
Combine Stock and Wine in a roasting pan. Place pan over medium heat, cook 3 minutes, stirring constantly. Set a roasting rack in pan.
Heat a large skillet over medium high. Add remaining 2 Tablespoons Oil. Place Loin in pan; cook 12 minutes or until browned. Place Loin on rack; cover loosely with foil. Roast for 50 minutes or until meat registers 150 degrees. Remove Pork from pan; let Pork stand 20 minutes. Swirl Butter into pan juices until butter melts. Cut Pork into 3/4 in. slices; serve with Au Jus.