if using tender asparagus spears (very thin and about 15-18cm long), cut 5cm (2 inches) below tips and keep separated.
simmer stalk sections in salted water for 3 minutes, then add tips and cook for 2 further minutes; drain and divide between two serving plates.
if using chunky, whole asparagus spears, remove the thick bottom section by holding each spear in your hands and bending towards the bottom until it snaps naturally; then proceed as for steps 1 and 2 above.
To make the Hollandaise sauce:
hand-whisk the egg yolk, salt, pepper and ACV over a bain-marie (water bath) until pale and dense; make sure your mixing bowl doesn't touch the simmering water below it.
add butter one cube at a time whilst whisking continuously; the sauce will get denser and more velvety-smooth as you keep adding butter; if it gets too thick for your liking, you can thin it with a little water.
adjust seasoning to your taste and pour immediately over your plated asparagus.
Notes
Asparagus will retain its vibrant green colour if you add ½ tsp bicarbonate of soda to the boiling water.
Metric kitchen scales are an inexpensive yet invaluable gadget to enable accurate measurement of ingredients. Store them upright in a cupboard or over your worktop and they'll only take up a tiny bit of space. Click HERE for the ones I use.