Set sous vide machine to 74C/165F.
Season chicken thighs with salt and pepper to taste. Place chicken in freezer bag with chicken stock, 2 Tbsp of butter, fresh lemon juice and rinsed capers. Remove the air through a vacuum sealer or the displacement method. Drop the bag in the bath for an hour and a half.
Remove bag from bath. Take chicken out of the bag and pat dry. Set the bag containing the liquids to the side for the sauce.
Heat up large skillet on medium high. Add 1 Tbsp of olive oil and 2 Tbsp of butter. When the butter and oil begin the sizzle, add in chicken thighs skin-side down for 1 minute, or until browned. Flip and cook other side for 1 minute. Remove chicken thighs from skillet, and place on plate to rest.
Add the liquids from the bag in to the skillet. Bring liquid to a simmer, and cook for 2 minutes. Return chicken back to the pan for 1 minute, and baste the chicken with the sauce. Remove skillet from heat, garnish with chopped parsley and enjoy!