Beat yolks, water, salt and pepper in top of a double boiler until
blended.
Place over just-simmering water, heat and beat until mixture
thickens and is custardlike - a minute or two.
Turn heat to low and add butter, a tablespoonful at a time, beating all the while. When all butter is added, remove sauce from heat and stir in lemon juice.
Serve hot over broccoli, cauliflower or asparagus.