Preheat oven to 375°F (190°C) with rack in lower third. Scatter celery, onions, lemon, and broth into the bottom of a roasting pan.

In a small bowl, whip softened butter with minced garlic, rosemary, sage, thyme, kosher salt, black pepper, and paprika.

Pat turkey breast completely dry with paper towels. Loosen skin from the breast meat with fingers. Rub 2/3 of herb butter under the skin directly on meat, and spread remaining butter over exterior skin.

Place turkey breast onto the vegetables in the pan. Roast at 375°F (190°C) for 65-75 minutes until an instant-read thermometer in the thickest part reads 162°F (72°C). Tent loosely with foil if browning too quickly.

Transfer to a cutting board and rest 15 minutes so juices redistribute (temperature will reach 165°F). Carve against the grain into thick medallions and serve with strained pan juices.