Wash the asparagus, cut off the woody ends. Cook the asparagus in boiling salted water for about 10 minutes
Wash the lemon hot, grate dry and cut the peel into thin strips with a zest ripper. Halve the fruit and squeeze the juice. Boil up lemon juice and stock. Gradually add butter cubes to the juice, stirring it with a hand blender until foamy. Add lemon zests to the sauce
Arrange asparagus, sauce and ham on a plate