Season both sides of the chicken thighs with salt and pepper.
Melt 2 tbsp of butter in a large cast iron skillet to high heat. When the skillet is very hot, place chicken thighs into the pan.
Brown the first side for 5-6 minutes. Flip the chicken, turn the heat down to medium and cook the chicken for an additional 8-10 minutes, until internal temperature reaches 165 degrees.
Remove the chicken from the pan and set aside on a plate.
Turn the heat down to low. Add the remaining 2 tbsp of butter, minced garlic, red pepper flakes and basil to the skillet. Stir together until garlic is fragrant and butter is melted.
Place the chicken back in the skillet and sprinkle 1 tbsp of parmesan cheese over each one. Using a spoon, spoon the butter sauce over each chicken thigh for about 1-2 minutes to coat the tops of the chicken thighs.
Place the chicken on a serving platter and pour the sauce over the chicken. Garnish with fresh basil.