1.To make hollandaise sauce, combine water, vinegar and pepper in a small saucepan; bring to the boil. Reduce heat; simmer, uncovered, until liquid is reduced to 1 tablespoon. Strain mixture through a fine sieve into a medium heatproof bowl; cool 10 minutes.
2.Whisk yolks into vinegar mixture. Set bowl over medium saucepan of simmering water (don’t let water touch base of bowl). Whisk mixture over heat until thickened. Remove bowl from heat; gradually whisk in melted butter in a thin, steady stream, whisking constantly until sauce is thick and creamy.
3.Boil, steam or microwave asparagus until tender. Serve asparagus on a large platter drizzled with hollandaise sauce; season to taste with cracked black pepper.