1. Butter and season a shallow tray and arrange the prepared fillets in a single layer.
2. Add the stock to barely cover the fish, cover with buttered greaseproof paper and poach in the oven at 175°C for 8 minutes.
3. Remove and place the fillets in a serving dish, cover and keep them warm.
4. Strain the cooking liquor into a shallow pan, add the bechamel and cream and reduce to a coating consistency.
5. Add the sabayon away from the heat, then pass through a fine strainer.
6. Whisk in the butter a little at a time, then add 50 g of the cheese and season with salt and cayenne.
7. Coat the fish evenly with the sauce, sprinkle with the rest of the grated Parmesan, glaze under a salamander grill and serve.