Place oven rack in the bottom third of the oven. Heat oven to 450°F.
Pat the skin of the turkey breast dry with paper towels and on roasting rack. Set aside. In a small bowl, combine garlic, butter, mustard, herbs, and salt. Mix until well combined, forming a paste.
Carefully loosen the skin from the turkey breast and rub the herb mixture on the meat under the skin. Pull the skin back to cover the turkey breast. Rub any remaining herb mixture over the skin
Place the turkey breast in the oven and lower the oven heat to 350°F . Roast the turkey breast for 1 hour, turning halfway. If the breast begins to brown too quickly, form a tent with foil. Check the internal temperature of the turkey breast at the 1-hour point, followed by every 10 minutes until it reaches an internal temperature of 165°F at the thickest part of the breast.
Remove the turkey breast from the oven and let rest for 10 to 15 minutes before carving.
If you have enough pan drippings, make gravy: Remove the rack, and place roasting pan directly over a burner set on high heat. Add 1 tablespoon unbleached all-purpose flour to pan, and whisk for 2 minutes, scraping up the pan drippings and incorporating all of the pan juices into the flour. Add 1/2 cup water, and continue whisking until a smooth gravy forms, about 2 minutes. Transfer to a gravy boat, and serve with turkey.