Mash the hard-boiled egg yolk, mix with oil, and add the slightly warmed puree of tomatoes, stirring constantly with a wooden spoon.
This sauce should be very thick and highly peppered.
You can thin it if you want to with a little oil, but keep on stirring as you do so to avoid separation.
Leave to get cold.
This is an excellent sauce to serve with cold hors-d'oeuvre.
Hors-d'oeuvre garnished with it may also be decorated with chopped hard-boiled egg.