Mix all the marinade ingredients together in a zip bag or a bowl. Let the chicken marinate covered in the refrigerator for at least 1 hour.
When ready to cook melt the butter in a skillet on high heat on the stove. Add the onions and cook for 10-15 until the onions turn golden brown. Remove the onions and set them aside. Leave the melted butter in the pan.
Add the chicken and marinade to your skillet to cook on high heat. Let the chicken cook on each side for 5-7 minutes so that the chicken crisps and gets those delicious golden brown spots.
Next, reduce the heat of your stove to medium and mix the tomato paste and cream into the skillet. Add the onions back to the skillet and let the chicken simmer in the sauce for 12-15 more minutes to allow the chicken to fully cook.
When the chicken is all done cooking remove your pan from the heat and garnish with cilantro. Serve your butter chicken with a side of cauliflower rice and a piece of keto naan bread.