75 g (3 oz) watercress, plus extra sprigs to garnish
1 tablespoon crème fraîche
Cook the pasta in a large saucepan of salted boiling water according to the pack instructions until al dente.
Meanwhile, make the watercress pesto. Tip the walnuts into a small frying pan and dry-fry over a medium heat for 3 minutes, giving the pan a shake every now and again, until they start to turn brown. Leave to cool for a minute or two. Place the nuts, watercress and crème fraîche in a small food processor or blender and whizz together to form a pesto. Season well.
Drain the pasta, then spoon into serving bowls and arrange slices of the cheese on top. Serve with dollops of the pesto and garnished with watercress sprigs.