Serves 4

Prep time 1 hr, cook 35 mins (plus resting, chilling)

For fish mousse, process fish in a chilled food processor, scraping sides down occasionally, until a very fine sticky paste forms. Place in freezer to chill (5 minutes), then, with motor running, add egg and eggwhite, scrape sides, then add cream, tarragon and lemon juice and process until just combined (do not overwork or mixture may split). Pass through a fine sieve, season to taste and refrigerate until required.

Lay trout fillets on a work surface. Spread 4 fillets with fish mousse, leaving a 1cm border (you may have some left over), then sandwich with remaining fillets. Lay each sandwich on a large piece of plastic wrap and roll tightly to form a cylinder (fold in sides halfway through rolling to seal ends), then refrigerate until firm (40 minutes-1 hour).

Meanwhile, for sorrel sauce, combine capers, basil, tarragon, parsley, anchovy, mustard, lemon juice, half the garlic and 60gm butter in a small bowl, refrigerate until required. Melt remaining butter in a small saucepan over medium heat, sauté shallot and remaining garlic until tender (2-3 minutes). Add vermouth and reduce slightly (1-2 minutes), add fish stock, bring to the boil over high heat, add spinach, stir until wilted (30 seconds), then transfer to a food processor and process until smooth. Meanwhile, blanch wood sorrel (15-20 seconds), add to food processor with caper butter mixture, process until smooth and combined, season to taste and keep warm.

Steam trout in a steamer placed over a saucepan of simmering water until just cooked through (8-10 minutes), then rest (1-2 minutes). Carefully remove plastic wrap, thickly slice trout, divide between serving plates, spoon over sorrel sauce, scatter with extra wood sorrel, season to taste and serve.