Cook the broccoli according to pack instructions. Meanwhile, to make the hollandaise sauce, put the lemon juice, vinegar and water into a saucepan and boil until reduced by half. Leave to cool. Put the egg yolk and reduced vinegar liquid into a basin over a pan of gently simmering water and whisk until thick. Gradually add the butter, a piece at a time, whisking after each addition. Season to taste and serve over the cooked broccoli. NOTES : A beautiful, rich buttery sauce which goes particularly well with broccoli and asparagus.