01 - Preheat the oven to 375°F. Pat the turkey breast completely dry with paper towels to ensure crispy skin.
02 - In a small bowl, combine softened butter, olive oil, chopped rosemary, thyme, sage, garlic, lemon zest, salt, and pepper. Mix thoroughly to form a cohesive herb paste.
03 - Gently loosen the skin from the turkey breast using your fingers. Rub half the herb paste underneath the skin directly onto the meat for maximum flavor penetration.
04 - Rub the remaining herb paste evenly over the entire exterior of the turkey breast, coating the skin completely.
05 - Arrange quartered onion, carrot chunks, and celery stalks in the bottom of a roasting pan. Pour 1 cup of chicken broth over the vegetables to create a flavorful base.
06 - Place the seasoned turkey breast skin-side up directly on top of the vegetable bed in the roasting pan.
07 - Roast uncovered for 1½ hours, or until the internal temperature reaches 165°F in the thickest part of the breast. Baste with pan juices every 30 minutes for added moisture and flavor.
08 - Transfer the roasted turkey breast to a serving platter. Tent loosely with aluminum foil and allow to rest for 15 minutes before slicing to retain juices.
09 - Strain the pan drippings through a fine mesh sieve, discarding the cooked vegetables. In a saucepan, melt 2 tablespoons butter over medium heat.
10 - Whisk cornstarch into the melted butter, stirring constantly for 1–2 minutes to form a smooth roux and cook out the raw starch flavor.
11 - Gradually whisk in 2 cups of broth and 2 tablespoons of reserved pan drippings, ensuring no lumps form.
12 - Simmer the gravy over medium heat, whisking continuously, for 5–7 minutes until thickened to desired consistency. Season with salt and pepper to taste.
13 - Slice the rested turkey breast and arrange on plates. Serve immediately with warm herb gravy ladled over the top.