Prepare a sous vide immersion circulator for use according to the manufacturer’s instructions. Preheat the water to 150°F.

Season the chicken with salt and pepper. Place the chicken in a vacuum-sealable bag. Add butter to the bag. Seal the bag tight and double it. Carefully place the bag into the water and cook for 2 hours.

War the oil in a large fry pan over medium heat. Remove the chicken from the bag and pat dry with paper towels. Place the chicken, skin side down, in the pan and cook until golden brown, about 10 minutes. The turn the chicken over and cook for another 2 minutes. Add juice from 1/2 lemon and serve with mashed potatoes or vegetables.