Preheat the broiler. Gut the mackerels, remove the heads, rinse thoroughly, and pat dry with paper towels.
Season the cavities with pepper. Brush with a little green pepper mustard and stuff with half the fresh herbs, rinsed and finely chopped.
Wrap each in aluminum foil papillotes. Broil for 15 minutes, turning halfway through cooking.
In a saucepan, mix the cream with the remaining mustard. Simmer gently over low heat. Off the heat, stir in 1 tablespoon chopped herbs.
Unwrap the mackerels. Sprinkle with remaining chopped herbs, crushed pink peppercorns, ground pepper, and Guérande fleur de sel. Surround with sauce.
Serve with a mix of white and wild rice.
