Season chicken pieces with salt and pepper. Heat oil, curry powder, and cayenne in a large skillet over medium-high heat for five minutes.
Stir in onions and garlic, and cook 10 minutes more or until onions are very clear.
Add chicken, tossing lightly to coat with curry oil. Reduce heat to medium, and cook for 7 to 10 minutes, or until chicken is no longer pink in center and juices run clear.
Add potatoes, then add coconut milk, tomatoes, tomato sauce, chopped cilantro, and sugar into the pan, and stir to combine.
Cover and simmer, stirring occasionally, for about 30-40 minutes or until sauce thickens. Serve with Jasmine rice and garnish with cilantro.