Cook the noodles in plenty of salted water until they are firm to the bite.
In the meantime, cut the 4 spring onions into rings and fry in butter. Add the lemon zest, crème fraîche, cream and sherry, add about 2 tablespoons of lemon juice. Simmer for 5 minutes, add salt and pepper. If necessary, add lemon juice or a little sugar to taste.
Mix with pasta and parmesan, or serve the cheese separately. Garnish with lemon balm if desired.