Melt 2 Tbsp. of the butter, and place chicken skin-side-down in the pan along with the remaining marinade. Cook until the chicken is browned on one side, 3 to 4 minutes, and then flip each piece over and cook 1 minute more. Sprinkle some of the lemon sugar and remaining ½ tsp. of ground pepper over the chicken and transfer skillet to oven. Roast until chicken is completely cooked through and a thermometer interested into the thickest part of the thigh reads 165°F, about 25 minutes.