This chic starter is a doddle to make, and something to really enjoy in spring when watercress is at its peak.
Blitz the trout, watercress, horseradish, butter, lemon juice, lemon zest and olive oil in a food processor until smooth. Divide half the mixture between two chef's rings, each placed on a separate plate.
Sprinkle over a few walnuts, and top up with the remaining trout mixture. Spoon over the Greek-style yoghurt, chill for a few minutes, then carefully remove the chef's rings. Garnish with watercress.
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