The definition of the sachertorte is very strictly regulated in Austria. We make no claims that our recipe would pass muster in its home country, but we think it a fine example of its kind. Adding the extra egg white makes a lighter cake. Please read About Tortes.

Have all ingredients at room temperature, about 70°F. Preheat the oven to 325°F. Grease and flour the bottom of a 9-inch springform pan and line with a round of parchment paper.

Grate:

Beat in a large bowl, or in a stand mixer with the paddle attachment, at medium-high speed until light and creamy, about 3 minutes:

Beat in one at a time:

Add the grated chocolate and:

Using clean beaters (or transfer the yolk mixture to another bowl, clean the stand mixer bowl, and switch to the whisk), beat in a large bowl at medium-high speed until stiff but not dry:

Fold one-quarter of the egg whites into the batter, then fold in the remaining whites. Scrape the batter into the pan. Bake until a toothpick inserted into the center comes out clean, 50 minutes to 1 hour.

Let the cake cool completely in the pan on a rack. Remove the sides of the pan and slice the torte horizontally into 2 layers. Should the top be mounded, reverse the layers so the finished cake has a flat top. Spread between the layers:

Cover the cake with:

For a really Viennese effect, garnish each slice with a great gob of schlag, or: