Crush the sunflower seeds then warm 50ml of the sunflower oil in a frying pan, add the sunflower seeds and toast until evenly browned. Add the remaining oil and allow to cool before passing through a fine sieve.
Whisk together the yolks, mustard, vinegar and salt, gradually incorporate the oil in a slow steady stream whilst whisking until a thick emulsion is achieved (If this consistency is reached before all of the oil is added loosen with a few drops of water). Check seasoning and adjust if necessary.
Break the asparagus spears by holding gently at each end and bending until it breaks at its tender point. At this point take all the tougher ends and juice them or blend with a little water and strain. Reserve the juice.
Heat a pan wide enough to contain all of the asparaguses in a single layer then add the butter followed by the asparagus, season with a little salt and cook until the asparagus just about starts to roast. At this point add the asparagus stock and add chicken stock to just cover the asparagus if necessary. Bring to the boil and cover with a lid or foil. Cook for 3 minutes then remove the lid and continue to boil until most of the liquid has reduced away and what is left forms and emulsion with the butter giving a nice glaze to the asparagus.
Serve a pile of the asparagus with a spoonful of the mayonnaise and some toasted sunflower seeds sprinkled over the top.