Preheat the oven: Set oven to 400°F (200°C). Lightly oil a large baking dish or sheet pan.
Season the chicken: Pat chicken thighs dry with paper towels. Rub with olive oil, melted butter, salt, and pepper.
Arrange in pan: Place chicken pieces skin-side up in the baking dish. Nestle pears, onion wedges, garlic, and thyme sprigs around the chicken.
Add liquid: Pour chicken broth (or wine) into the pan to keep the dish moist during roasting. If using, drizzle with balsamic vinegar for added brightness.
Roast: Place in the oven and roast for 35–40 minutes, or until chicken reaches an internal temperature of 165°F (74°C) and skin is crispy and golden brown.
Caramelize finish (optional): For extra crispiness and caramelization, broil on high for 2–3 minutes at the end, watching closely.
Serve: Spoon pan juices over the chicken and pears before serving. Garnish with fresh thyme leaves.