Heat 1 tablespoon of the olive oil in a medium saucepan and cook the onion, shallots, and garlic over low heat until softened, about 5 minutes. Put the flour in a plastic food bag and add the monkfish cubes. Shake to coat. Heat 2 tablespoons of the remaining olive oil in a flameproof casserole or dutch oven and cook the monkfish until golden, about 10 minutes, turning occasionally. Drain off any water which accumulates in the pan and add the remaining olive oil. Heat the Cognac in a small saucepan and light it with a match. Pour the burning cognac over the fish. It will burn out on its own. Stir in the white wine, tomatoes, tomato purÄe, sugar, Cayenne pepper, and bouquet garni. Season with salt and pepper. Bring to a boil, cover, reduce heat and simmer for 20-25 minutes.
