Trim the ends of the white asparagus and peel the skin from the tip to the base using a peeler. Cut them in half.

Boil 1000ml of water in a pot, add the asparagus peels, salt, and lemon juice. Add the asparagus and simmer for 5–15 minutes depending on thickness. Skim off any foam.

Place butter in a microwave-safe container and heat at 600W for 30 seconds until melted.

Set a bowl over a double boiler, add egg yolk, lemon juice, and salt. Whisk until thickened to a mayonnaise-like consistency.

Gradually add melted butter to the egg mixture, whisking continuously until smooth.