As a seasoned chef with years of French seafood expertise, here's how to prepare this elegant dish:
Poach the skate fins in a court-bouillon made with the bouquet garni, coarse sea salt, peppercorns, clove, sliced onion, and 2 liters of water. Drain, then carefully flake the flesh using a thin knife along the edges. Set aside.
Meanwhile, peel and cook the potatoes in milk with the peeled, degermed garlic cloves. Add a splash of water if needed to cover, and season with salt and pepper.
Grate the Parmesan cheese finely.
Mash the potatoes and garlic smooth with a potato masher. Stir in the fresh cream until incorporated, then add the butter while mixing vigorously. Taste and adjust seasoning.
Butter a shallow baking dish generously. Layer the flaked skate evenly on the bottom, top with the garlic mash, and sprinkle grated Parmesan over the surface.
Bake at thermostat 7/8 (200°C) until the top is beautifully golden and bubbling.
Serve directly from the dish for a stunning presentation.
