Smoked trout has a more delicate flavour than ... For the watercress purée, bring a saucepan of salted water up to a rolling boil, then add the watercress and cover the pan with a lid.

Add around 100ml/3½fl oz of the pasta water and stir together. Mix in the crème fraîche, lemon zest and juice until everything is combined. Finally stir through the smoked salmon and rocket.