The plush richness of Sachertorte is due to the addition of butter and melted chocolate, but for many mixtures, the egg yolks are creamed with sugar. Traditionally, flour or other dry ingredients and meringue are folded in in alternating batches. This results in a light, moist sponge.
Prepare the meringue and set it aside. Beat the yolks into the creamed butter and sugar gradually, then fold in the cooled melted chocolate.
Fold roughly one third of the meringue and half the sifted cornflour into the creamed mixture. In batches, fold in half the remaining meringue, the cornflour, then the rest of the meringue.