Cook the pasta in plenty of boiling salted water for 10 minutes. In the meantime, wash the lemon hot and dry. Finely grate the peel and put aside. Then peel the lemon so that the white skin is completely removed.
Cut out the flesh between the dividing skins and chop it finely. Bring the cream and lemon fillets to the boil in a saucepan and boil for about 5 minutes until the sauce thickens. Season to taste with salt and pepper.
Stir in cheese and egg yolk. Drain the pasta and arrange on plates with the sauce. Sprinkle with lemon zest and garnish with lemon balm.