Blend the scallions, onions, thyme, garlic, ginger, and one Scotch bonnet in a food processor or with a hand-held blender. Throw in a little water or oil if it needs a little liquid during the pulsing. Blend until the ingredients are fully combined.
Marinade the Chicken
Cut up the chicken into large pieces and marinade with the sauce for at least an hour. Overnight is preferable.
Cooking the Curry
In a braiser (or another high-walled pan), toast the curry and cumin over low heat until it becomes aromatic.
Add the marinaded chicken (plus any additional marinade) and potatoes into the pan and mix with the curry and cumin. Sprinkle it with salt and pepper.
Pour the chicken stock over the chicken and potatoes until the chicken is covered. Top it with a little water if necessary to reach this point.
Cover the braiser and bring the stock to a boil, then simmer over medium heat for 25 minutes.
Uncover and stir in the other chopped Scotch bonnet pepper (this is optional - only if you want it real spicy).
Pour in about 1/2 to 1 cup of additional water to loosen the ingredients, and cook uncovered for 20 to 30 minutes or until the chicken is tender and the liquid in the pan is of a gravy thickness.
Serve with rice.
If you're having trouble finding Scotch bonnets, you can use habanero peppers instead. They are typically easier to find, but not quite as sweet.