Preheat the oven. Set your oven to 400°F (200°C).
Pat the chicken thighs very dry with paper towels. Dry skin is key to crispness.
Season the chicken. In a small bowl, mix salt, pepper, paprika, and Italian seasoning. Rub the mixture evenly under and over the skin of each thigh.
Heat the pan. Place a large oven-safe skillet (cast iron works best) over medium-high heat.
Add the olive oil and 2 tablespoons of butter.
Sear skin side down. When the butter is foamy and hot, add the chicken thighs skin side down. Press gently with a spatula for even contact. Sear without moving them for 6–8 minutes, until the skin is deep golden and crisp.
Flip and sear briefly. Turn the thighs and cook for another 2 minutes on the second side to develop color.
Add garlic and butter. Turn the heat to medium-low.
Add the remaining 2 tablespoons of butter and the minced garlic to the pan, stirring the garlic in the butter for about 30 seconds. Spoon some of the garlicky butter over the chicken.
Top with Parmesan. Sprinkle the grated Parmesan and red pepper flakes (if using) evenly over the chicken and into the pan drippings.
Finish in the oven. Transfer the skillet to the preheated oven. Roast for 12–16 minutes, until the thighs reach an internal temperature of 175–185°F.
Higher than 165°F is ideal for thighs; the extra heat melts connective tissue and keeps them tender.
Add lemon and herbs. Remove from the oven, squeeze lemon juice over the thighs, and shower with chopped parsley. Let them rest for 5 minutes so the juices settle.
Serve. Spoon the pan juices over the top and add extra Parmesan if you like. Serve with a green salad, roasted broccoli, buttered noodles, or mashed potatoes.