• To make the stuffing, melt the butter over medium-high heat, then add the garlic and sauté it for about 30 seconds (make sure not to burn it, or it will become bitter). Add the sliced leeks and sauté until soft (about 5 minutes).
• Add the sliced mushrooms, increase the heat to high, and cook until soft and all liquid has evaporated (about 10 minutes). Remove from the heat and add the breadcrumbs, cheese, one teaspoon each of parsley, sage, rosemary and thyme, 1 teaspoon salt and 1/2 teaspoon pepper. Set aside.
• To make the herb butter, use a fork to combine the tablespoon of softened butter with 1/2 teaspoon each of parsley, sage, rosemary and thyme. Set aside at room temperature.

For the turkey:

• Preheat the oven to 350 degrees. Butterfly the turkey breast open with a very sharp knife and place it skin side down on a cutting board. Cover it with plastic wrap, then pound it out lightly with a meat mallet to flatten it a bit and make it an even thickness.
• Remove the plastic wrap and sprinkle the turkey breast with salt and pepper. Spread the stuffing onto the side without skin and spread it all over, leaving about 3/4-inch on each edge. Roll the turkey breast up as tightly as possible, finishing with the skin side up (towards you).
• Rub the entire top surface with the herb butter, placing some butter under the skin, if possible. Using butcher’s twine, tie up the turkey breast to keep its shape while roasting. Place the stuffed turkey breast on a roasting pan or on a baking rack that has been sprayed with nonstick cooking spray.
• Roast the breast, uncovered, until the stuffed turkey reaches an internal temperature of 165°F, (about 1 1/2 hours). [Check the turkey about halfway through and cover it with a piece of foil if the top begins to get too brown].
• Once it has finished, remove from the oven and let it sit, covered with foil, for about 15–20 minutes before slicing. Snip off the butcher’s twine, and serve.