(For stuffed tomatoes, cold meat or potato salad.)
Melt a large tablespoonful of butter. Add a saucer of vinegar to
the yolks of two eggs. Then add a teaspoonful of dry mustard and a
teaspoonful of sugar. Stir the mixture—sugar and eggs—into the vinegar;
then add it to the butter which you have on the stove, melting. Keep
stirring this until it gets thick, and remember that it will be much
thicker when it is cold. In case you wish to use this for potato salad,
don’t make it very thick.