Preheat your oven to 400 degrees F. Pat the chicken thighs completely dry with paper towels on both sides, especially the skin. Moisture is the enemy of a crispy crust, so take an extra 30 seconds here. Season all over with salt, pepper, and smoked paprika.

Set a 12-inch cast iron skillet over medium-high heat and add the oil. Let the pan heat for about 2 minutes until the oil shimmers and just starts to smoke lightly. Place the chicken thighs skin-side down in the pan. Do not move them. You should hear a strong sizzle the moment they hit the pan. If you do not, the pan is not hot enough.

Cook skin-side down for 8 to 10 minutes without touching them. You want the skin to release naturally from the pan when it is ready. If it feels stuck, give it another minute. Once the skin is deep golden brown, flip the thighs and cook the other side for 3 minutes. Transfer the skillet to the oven and roast for 15 to 18 minutes, until a thermometer inserted near the bone reads 165 degrees F.

Remove the chicken to a plate and tent loosely with foil. Pour off all but about 1 tablespoon of the drippings from the skillet, leaving the browned bits on the bottom. Set the skillet back over medium heat on the stovetop and add 2 tablespoons of butter. Once it melts, add the minced garlic and cook for about 1 minute, stirring, until it smells fragrant but has not browned.

Pour in the chicken broth and use a wooden spoon to scrape up all the browned bits from the bottom of the pan. Those bits are pure flavor. Let the sauce simmer for 3 to 4 minutes until it reduces slightly and looks a little glossy. Add the lemon juice and the remaining 2 tablespoons of butter, swirling the pan until the butter melts and the sauce comes together.

Taste the sauce and add salt or a little more lemon juice if it needs it. Return the chicken thighs to the skillet, skin-side up, and spoon the sauce over them. Scatter the parsley on top and serve immediately. The skin stays crisp as long as you keep it facing up and do not cover the pan.