Preheat oven to 325°F. Pat turkey breast dry. Rub softened butter all over the skin and underside where possible. Season generously with salt and pepper. Add turkey to a roasting pan along with onion, potatoes, and turkey stock. Roast uncovered for 45 minutes to start. If skin browns too quickly, cover loosely with foil.
While turkey roasts, prepare pomegranate glaze: In a small saucepan over medium heat, add POM Wonderful 100% Pomegranate Juice, honey, apple cider vinegar, salt, cinnamon, pepper, and cloves. Simmer for 10 minutes until slightly thickened and glossy.
Remove turkey from oven and brush generously with half of the glaze. Return to oven and continue roasting for 30 minutes. Cook until internal temp reaches 165°F in the thickest part. Let turkey breast rest 15 minutes before slicing. Transfer to a serving platter and spoon remaining glaze over top. Garnish with POM Wonderful Pomegranate Arils and fresh thyme.