To make the stuffing, tear the bread into small pieces and add it to a food processor. Pulse until breadcrumbs the size of peas have formed. Remove from the food processor and add it to a large mixing bowl.

Add the sage, rosemary, parsley and garlic to the food processor and pulse until finely chopped. Add it to the mixing bowl with the breadcrumbs.

Add the carrot, celery and onion to the food processor one at a time, pulsing until finely chopped. Add the vegetables to the mixing bowl followed by the chicken stock, melted butter, salt and pepper. Mix to combine and set aside.

Preheat the oven to 375 degrees F.

To prepare the turkey breast, lay it out flat onto a large cutting board, skin-side down. Use a sharp knife to butterfly the turkey breast in areas where it may be thick. You want to make the turkey breast as even in thickness as possible. Place a sheet of parchment paper on top of the turkey breast and pound with a meat mallet or rolling pin until the thickness is even. Remove the parchment paper and discard.

Add the stuffing onto the turkey breast and spread it out in an even layer. Roll the turkey breast in a tight roll so that the skin is on the outside. Tie with butchers string every inch and then place in a roasting pan.

Use a paper towel to dry the skin of the turkey breast and then cover the entire turkey breast evenly with butter, salt and pepper.

Add the quartered onions to the bottom of the roasting pan, followed by the chicken stock. Place the turkey in the middle of the oven, uncovered, and bake for 30 minutes.

After 30 minutes, reduce the heat to 350 degrees F and continue to cook until the turkey has reached an internal temperature of 160 degrees F, about 1 ½ hours. Remove the turkey from the oven, cover with aluminum foil, and let it rest for 20 minutes to allow the juices to redistribute, and for the turkey to reach an internal temperature of 165 degrees F. Then, use a sharp knife to slice the turkey into slices and add to a serving platter with the cooked onions.

To make the gravy, add the dripping from the pan into a small pot along with the chicken stock and bring to a boil. In a small bowl, combine the cold water with the cornstarch and mix until there are no lumps. Add the cornstarch to the pot and whisk to combine. Once the gravy has thickened, season with salt and pepper and serve.