Melt 2 tablespoons of the butter in a large cast-iron skillet over high heat.
Season the chicken thighs with salt and pepper evenly on both sides.
When the skillet is hot and butter just begins to brown, add the chicken thighs, skin-side down. Allow them to cook for 5 minutes without touching, then flip and cook them for 5 more minutes.
Turn off the heat, then add the sliced garlic and the rest of the butter to the skillet.
Transfer the skillet to the preheated oven and roast on middle rack for 25 to 30 minutes, or until the chicken reaches 200 F in the center.
Garnish with chopped parsley and serve with plenty of garlic butter and crunchy garlic pieces.