With turkey skin side down, use a knife to score down the long oblong bone in center of breast. (epicurious.com)
Using the heels of your hands, press down on the center of both breasts until you hear a cracking sound and the bird flattens. (tastingtable.com)
Turn the turkey over, breast side up, and press down hard with the heels of your hands in the center of the breast to flatten — it will crack. (thespiffycookie.com)