In a small bowl, combine the SWEET CURRY, CAYENNE (if using) and 2 TB. of the water. Let stand for 5 minutes.
Heat the oil or butter over medium heat. When hot, add the onion and cook for about 3 minutes or until the onions start browning and everything smells really good.
Add the curry/water mixture; stir quickly.
Add the chicken and sauté quickly for a few minutes until well coated, then add the remaining water and stir well.
Reduce the heat to a simmer and cook for 20 minutes, stirring every 5 minutes or so.
Reduce the heat to very low and stir in the yogurt, if using.
Taste and add salt as desired.
