Season the chicken thighs with the salt and pepper and place them, skin side down, in a cold cast iron skillet.
Turn the skillet on medium low heat and let the thighs cook about 10-12 minutes, until the skin is crisp. Remove from heat and set aside.
Heat the butter in the Instant Pot on the sauté setting. Add the onions and garlic and cook until they are softened, about 3-5 minutes.
Add the chicken broth, lemon juice, lemon zest and cayenne pepper. Mix together.
Nestle the chicken thighs on top and close the lid. Set the Instant Pot to pressure cook on high for 10 minutes.
Let the pressure release naturally for 10 minutes then use the quick release to release any remaining pressure.
Carefully remove the thighs from the Instant Pot and set them aside.
Add the cream and bring to a simmer on the sauté setting. Simmer for about 5-7 minutes, until slightly reduced.
Add any additional salt to taste at this time.
Add the chicken back in and spoon the sauce over to coat the chicken. Serve garnished with chopped parsley.