1. Prepare the Brussels sprouts: trim the stem, make a small incision, remove any damaged outer leaves. Rinse in vinegar water. Bring salted water to a boil, poach the Brussels sprouts for 5 minutes. Cook them in a second pot of boiling salted water for 15 minutes. Drain and squeeze.
2. Cut the rabbit fillets in half. Heat 2 teaspoons of margarine in a non-stick skillet, sauté the fillets for 5 minutes, turning them halfway through cooking. Season with salt, pepper, and sprinkle with ground juniper berries. Keep warm between two plates.
3. Peel and chop the shallot. Mix the heavy cream and mustard. Heat 1 teaspoon of margarine in the skillet, sauté the shallot and bacon for 2 minutes. Add the Brussels sprouts and sauté for 2 minutes while stirring. Pour in the mustard cream and mix for 1 minute over low heat. Adjust the seasoning with salt and pepper. Pour the mixture into a shallow dish, place the rabbit fillets on top.