Preheat your grill on high for at least 10 minutes.
Add butter to a small microwavable bowl and microwave until melted and bubbling. While the butter is still hot/warm, stir in ½ teaspoon black pepper, garlic, and parsley. Then stir in the parmesan.
Add chicken to a medium bowl and season all over with the salt and remaining ½ teaspoon pepper and rub around to coat. Add 2 tablespoons of the parmesan butter and toss to coat.
Transfer another 2 tablespoons of the parm butter to a small bowl (we’ll use this after the chicken is done).
Add the chicken to the hot grill and grill for 3-5 minutes or until you have grill marks. Flip the chicken and brush with the remaining parmesan butter. Cover and grill for another 2-4 minutes or until cooked through and you have some grill marks on the other side.
Transfer to a cutting board, let it cool for 5 minutes, then spoon the reserved parm butter over each thigh and gently spread to coat. Serve right away with your choice of side.