Preheat the oven: Set your oven to 425°F (220°C).
Line a rimmed baking sheet with foil or parchment for easy cleanup. Place a wire rack on top if you have one.
Pat the chicken dry: Use paper towels to remove excess moisture from the thighs. This helps the skin crisp up.
Season both sides lightly with salt and pepper.
Mix the sauce: In a bowl, combine mayonnaise, Parmesan, Dijon, lemon juice, garlic, onion powder, smoked paprika, 1/2 teaspoon salt, 1/2 teaspoon pepper, and olive oil. Stir until smooth. Fold in herbs if using.
Coat the chicken: Place the thighs skin-side up on the rack or sheet.
Spread a generous layer of the sauce over the top and a thinner layer underneath. Keep most of it on top to create a flavorful crust.
Bake: Roast for 30 to 40 minutes, depending on size. The chicken is done when the thickest part reaches 175°F to 190°F and the juices run clear.
Thighs shine at higher temps because the connective tissue melts and turns silky.
Broil for extra color (optional): If you want a deeper golden top, broil on high for 1 to 2 minutes. Watch closely to avoid burning.
Rest and serve: Let the chicken rest for 5 minutes. Scatter parsley on top and serve with lemon wedges.
The acidity brightens the rich flavors.