Remove turkey breast from its packaging and place on a large plate. Pat dry on all sides with clean paper towels. Sprinkle the turkey generously with kosher salt and black pepper, then place it on the rack of a roasting pan, skin side up.
Preheat the oven to 325 degrees F and be sure a rack is near the bottom, with plenty of space above it.
In a small bowl, mix together the softened butter, garlic, sage, rosemary, and thyme.
Using the back of a spoon or your fingers, gently loosen the skin of the turkey breast. (Try not to slice or tear the skin as you do this.) Spread about 2 tablespoons of the butter mixture under the skin, then rub another 3-4 tablespoons of the butter over the top, sides, and bottom of the turkey breast. Note there should be roughly 2 tablespoons of the butter mixture remaining in the bowl.
Sprinkle the turkey again, lightly, with salt and pepper. If desired, stuff the cavity in the turkey’s underside with an onion, halved or quartered, garlic cloves, cut orange or lemon wedges, and a few sprigs of herbs.
Place turkey in the oven and bake, uncovered, until the internal temperature reaches 165 degrees F. Melt the remaining butter mixture and baste or brush it on top of the turkey breast every 30-40 minutes as it bakes. (You can estimate roughly 20 minutes per pound, so for example, a 6 pound breast should require at least 2 hours, but cooking times for turkey are truly just a ballpark range. Using a thermometer is by far the best method.)
Remove turkey from the oven and let it rest for 15-20 minutes, then carve and serve as desired.