Whisk the 5 eggs and gradually pour in the butter while stirring nonstop, as well as the lemon juice.
After 5 min, add the aged, very finely grated cheese. Continue beating for another 5 min.
Season the sauce with black pepper and chopped parsley that you've dried from the moisture very well.
If the cheese sauce ends up too thick, you can dilute it with a little water or lemon juice.