Heat the oil in a large sauté pan with a lid over medium-high heat. Add the onions and fry for 8–9 minutes, stirring a few times, until caramelized and soft. Decrease the heat to medium and add the garlic, harissa, paprika, chicken, 1 teaspoon salt, and a good grind of black pepper. Cook for 5 minutes longer, stirring frequently, then add the tomato puree and tomatoes. Add the water, bring to a boil, then simmer over medium heat, covered, for 30 minutes, stirring every once in a while.
Add the peppers and chocolate and continue to simmer for 35–40 minutes, with the pan now uncovered, stirring frequently, until the sauce thickens and the chicken is falling apart. Remove from the heat and stir in the cilantro. If you are serving the chicken as it is (as a stew without the batter), it’s ready to serve (or freeze, once it has come to room temperature) at this stage. If you are making the corn crust, spoon the chicken into a ceramic baking dish—one with high sides that measures about 8 x 12 inches/ 20 x 30 centimeters—and set aside.
Preheat the oven to 400°F.