Preheat oven to 400°F.
Chop onion, carrot and celery into large chunks and place in bottom of roasting pan. Set aside.
Remove skin from breast keeping in one piece. Reserve. Butterfly breast by cutting almost in half horizontally. Open like a book. Season both sides generously with salt and pepper.
With skin side down. Spread stuffing evenly over breast. Leave about 1/2 inch boarder free of stuffing around the edges. Take the top long edge and start to roll towards you. Roll into a log keeping it as tight as possible. Roll so it sits seam down.
Spread half of the butter and parsley mixture over the top and sides of the roll.
Drape skin on top of butter mixture spreading it out as much as possible. It won't cover the entire roll but that's okay.
Cut 5-6 pieces of butcher's twine to about 8"-10" lengths. Slide one piece at a time under the roll and tie at even spaces.
Spread the rest of the butter mixture on top and sides of roll.
Carefully move the roll to sit on top of the vegetables in the roasting pan. Pour in 1/2 cup chicken stock, reserving the other 1 cup for later.
Bake in preheated oven for 1 hour and 20-30 minutes or until an instant read thermometer reaches 165°F
When done, remove the turkey from roasting pan and reserve on a plate or cutting board loosely tented with foil. Let rest for 10-15 minutes.