Preheat oven to 425°F (220°C). Place your oven-safe skillet or roasting pan in the oven while it preheats if using cast iron. Pull the chicken from the refrigerator 15 minutes before cooking.
In a small bowl, combine softened butter, 2 tablespoons fresh rosemary, garlic powder, onion powder, paprika, 1 teaspoon kosher salt, and black pepper. Mix until smooth and well combined.
Pat the chicken thighs completely dry with paper towels on both sides. Gently loosen the skin from the meat and push about 1 teaspoon of herb butter under the skin of each thigh. Rub any remaining butter all over the outside. Drizzle with 1 tablespoon olive oil and rub to coat evenly.
In a large mixing bowl, combine halved potatoes, apple wedges, onion wedges, and smashed garlic cloves. Drizzle with remaining 2 tablespoons olive oil, add fresh thyme, a generous pinch of salt, and black pepper. Toss thoroughly to coat evenly.
Spread the vegetable and apple mixture in a single, even layer across the bottom of your roasting pan. Pour white wine or chicken broth around the edges of the pan.
Place the seasoned chicken thighs skin-side up directly on top of the potato and apple mixture. Roast in the preheated oven for 40 to 45 minutes, or until skin is deep golden brown and internal temperature reaches 165°F.
At the 25-minute mark, baste the chicken with pan drippings and gently stir the potatoes and apples to flip them for even browning. If skin is browning too fast, tent loosely with aluminum foil.
Remove from oven and let chicken rest in the pan for 5 minutes. Serve the chicken on top of the roasted potatoes, apples, and onions. Spoon pan drippings generously over everything just before serving.