Whisk together sauce ingredients in a small mixing bowl and set aside.
Place a large oven-proof skillet over medium heat, and add the butter. Once melted, place chicken, skin-side down, into the pan. Sear both sides of the chicken until the skin is golden brown and crispy, about 3 minutes per side.
Remove the skillet from the heat. Turn chicken skin side up (if it's not already), and cover with sauce.
Put the skillet in the oven and roast for 25-30 minutes until the chicken is cooked through (165 degrees F internal temperature).
Turn the oven on to broil, and cook for 2-3 minutes to crisp the chicken skin and further caramelize the sauce.
Remove from the oven. Serve the chicken from the skillet or plate it, and then garnish with peanuts and cilantro before serving warm.
Notes
If you don't have an oven-safe skillet, transfer the seared chicken to a baking dish and pour the sauce over top. Then, bake and broil as directed.