1. Chop the chiles coarsely. Heat the oil in a wide pot; add the onion and cook over medium-low heat, stirring frequently until softened, about 4 minutes. Add the coriander, cumin, garlic, and potatoes, followed by the chile along with 1/2 teaspoon salt and give a stir. Cook together of a few minutes, then add the water or stock. Bring to a boil, then lower the heat to a simmer.
2. Cook and cover until the potatoes are completely softened, about 25 minutes. Taste and season with salt and pepper. At this point you can mash the potatoes, or at least a few of them to give the dish a creamy sort of background, if desired.
3. Pour into a bowl, and add the cilantro. (I also add a squeeze of lime)