Pat the monkfish cubes dry. Season lightly with salt and pepper.
Into a sauté pan, heat the oil and butter over medium-high heat. Brown the monkfish cubes on all sides.
Add the cognac and light it with a flame and flambé. Take the pan off the heat, and remove the fish. Set aside.
Put the saute pan back on medium heat, and add the shallots and garlic. Cook until soft and stir often. Add the diced tomatoes, the tomato paste, the white wine, bouquet garni, cayenne pepper, salt, and pepper. Bring to a light boil and let simmer gently for 20 to 25 min or until the sauce is reduced and its flavor is concentrated.
Put the monkfish back into the sauce, cover, and cook gently for 10 min or until the fish is cooked through but still tender.
Remove the bouquet garni. Sprinkle some parsley, scallion, and served with some steamed vegetables or rice.