Preheat oven to 400 degrees F.
Season chicken thighs with salt and pepper, to taste.
Place a large cast iron skillet over medium high heat, and add 3 tablespoons of butter. When butter has melted, add the seasoned chicken, skin-side down, and sear on both sides until golden brown, about 2-3 minutes per side. Set aside.
Add the remaining 3 tablespoons of butter to the skillet and melt. Add garlic and cook for about 1-2 minutes, stirring frequently.
Remove skillet from heat and stir in Sriracha sauce and brown sugar until melted. Return chicken to the skillet, skin side up.
Place into the hot oven and roast until completely cooked through about 25-30 minutes.
Garnish with chopped parsley and serve.