Melt one stick of butter. Pour in one ounce lemon juice. Separate one egg and whisk the yolk into the butter and lemon. Put the whole thing in a (real or improvised) double boiler and stir while heating just until 160°F/70°C. My brother and I made this to dip some steamed artichokes in. It was plenty. Leftovers can be refrigerated and reheated very cautiously.

... You know what needs that egg white? WatermelonSorbet does. Or you could make two meringues out of it.