Mousse de Poisson — Cold Fish Mousse

Ingredients

• 400 g raw fish flesh, salmon for colour, sole for purity, or pike for tradition — skin and pin-bones removed
• 150 ml fish velouté, thick, well-reduced
• 200 ml fish fumet or aspic, strong, warm
• 8 g leaf gelatin, bloomed in cold water before use
• 200 ml double cream, softly whipped to just-holding peaks
• 1 tbsp dry vermouth, Noilly Prat preferred
• To decorate
• as needed cucumber, thinly sliced
• as needed chervil, picked into small sprigs
• as needed aspic, cooled to near-setting point, for glazing
• For the mould
• as needed neutral oil, for lightly oiling the mould

Method

1. 1
   Process the raw fish flesh in a food processor until completely smooth. Pass the purée through a fine tamis twice, pressing firmly with a plastic scraper until nothing remains above the mesh but dry fibre. The result should be almost liquid in consistency. Any fibre or visible lump remaining is unacceptable at this stage.
2. 2
   Season the purée firmly — approximately 20 per cent more than tastes correct at room temperature, as cold suppresses flavour perception. Transfer the purée to a bowl set over ice and stir in the thick fish velouté until fully combined.
3. 3
   Bloom the leaf gelatin in cold water until fully softened, then dissolve it in the warm fumet or aspic. Stir the gelatin-enriched fumet into the fish and velouté base. Add the dry vermouth. Continue to stir the mixture over the ice bath until it begins to thicken and the temperature approaches 15–20 °C. This is where the dish lives or dies: too warm, and the gelatin cannot hold the incorporated air; too cold, and the gelatin has already begun to set and the cream will not integrate smoothly — the window is narrow and must be judged precisely.
4. 4
   At the moment the base reaches its setting point and coats the back of a spoon with a light, trembling body, fold in the softly whipped cream in two additions. The cream must hold its shape but not be stiff — over-whipped cream produces a granular, heavy texture. Fold with a wide spatula using long, slow strokes until no white streaks remain and the mousse is uniformly pale and aerated.
5. 5
   Pour the mousse into a lightly oiled mould — ring mould, dariole, or terrine. Smooth the surface with a palette knife. Cover and refrigerate for at least 4 hours, or overnight. The gelatin requires this time to set fully; a shorter chill will prevent clean slicing and risk collapse on unmoulding.
6. 6
   To unmould, dip the base of the mould in warm water for 5 seconds — no longer. Invert onto the serving plate and give a single sharp downward shake. The mousse should release cleanly and hold its shape without slumping. Decorate with cucumber slices and chervil. Spoon over a thin mirror of near-set aspic and return briefly to the refrigerator to set the glaze. The finished mousse slices cleanly, holds its form on the plate, and melts without resistance on the tongue.