Preheat and prep: Heat the oven to 400°F (200°C).
Pat the chicken thighs very dry with paper towels. Dry skin is key to getting crisp.
Season well: In a small bowl, mix salt, pepper, smoked paprika, and onion powder. Sprinkle the blend evenly over both sides of the thighs, focusing on the skin.
Sear the chicken: Heat a large oven-safe skillet over medium-high.
Add olive oil and 1 tablespoon butter. When hot, place thighs skin-side down. Cook without moving for 6–8 minutes until the skin is deeply golden and crisp.
Flip and baste: Turn the thighs.
Add 2 tablespoons butter to the pan along with minced garlic and red pepper flakes. Stir the garlic around the chicken for 30 seconds, then spoon some garlicky butter over the tops.
Deglaze: Pour in chicken broth and lemon juice, scraping up browned bits for extra flavor. Let it bubble for 1 minute to meld.
Oven finish: Transfer the skillet to the oven.
Roast for 12–15 minutes, or until the thickest part of a thigh hits 175–185°F (79–85°C). Dark meat shines at a slightly higher temp, staying juicy and tender.
Final butter and herbs: Remove from the oven. Add the last tablespoon of butter and the parsley.
Tilt the pan and spoon the glossy sauce over the chicken. Sprinkle Parmesan if using.
Rest and serve: Let the thighs rest for 5 minutes. Serve with lemon wedges and drizzle with extra pan sauce.