Rinse the lemon with hot water, dry it and scrape off the peel with a zest zipper. Squeeze the lemon. Slowly bring the cream to the boil over a low heat. Gradually add the lemon juice. Season the cream with broth, salt and pepper. In the meantime, cook the spaghetti al dente. Mix the egg yolks and a little lemon cream and stir into the lemon cream. Put the sauce briefly on the hob, but do not boil any more. Pluck the basil leaves and stir in, cut into strips. Serve the sauce with the drained spaghetti.