How to Make It
In an enameled cast-iron casserole, combine the onions and butter with 1 1/2 cups of water and bring to a boil. Season with salt and pepper, cover and cook over moderate heat until the onions are softened, 10 minutes. Uncover and cook over moderately low heat, stirring, until the onions are soft and just beginning to caramelize, 40 minutes longer. Add a few tablespoons of water as the pan dries out. The fonduta will be thick and creamy.
Meanwhile, in a small bowl, combine the yogurt with the dill and 1 tablespoon of cilantro. Season with salt and pepper.
In a bowl, mix the flour, semolina, harissa, cumin, allspice and juniper with 1 tablespoon of salt. Soak the fish in the buttermilk for 5 minutes. Drain and dredge the fillets in the flour mixture and transfer to a wax paper-lined baking sheet.
In a very large skillet, heat 1/4 inch of oil. Fry the fish in batches over moderate heat, turning once, until golden and just cooked through, 6 to 8 minutes. Drain the fish on paper towels and transfer to plates. Serve with the fonduta and yogurt.
Roasted cauliflower and shaved fennel.