Sacher Torte is known around the world as a specialty of Vienna (at the Hotel Sacher) but is commonly found in pastry shops and in the kitchens it is sure to delight the chocolate lovers in your household. It will keep well for a few days in a cookie tin without refrigeration but for longer storing time do refrigerate. You can also bake and freeze the cake layer in advance. Defrost and assemble and glaze the torte before serving.
For the torte
6 ounces butter, plus 1 tablespoon for the cake pan
¾ cup sugar
5 ounces semisweet chocolate, melted and lukewarm
5 large eggs, separated
1 cup all-purpose flour, plus a bit for the cake pan
For filling and glazing the torte
2 cups apricot preserves
⅔ cup light corn syrup
2 tablespoons dark rum
2 tablespoons water
10 ounces semisweet chocolate, chopped in small chunks
Butter the bottom of the cake pan, cover it with the parchment, then butter the top of the paper and the sides of the pan. Heat the oven to 375°.
Cream the butter and sugar in the bowl of the electric mixer using the whisk attachment until light and smooth. Incorporate the egg yolks, one at a time, and then pour in chocolate gradually, mixing it in thoroughly and scraping the sides of the bowl as needed. On low speed, incorporate the flour. Whip the egg whites by hand (or by machine, in a clean bowl with a clean whisk) to stiff peaks. Fold the egg whites into the batter with a rubber spatula. Scrape the batter into the prepared cake pan and spread in an even layer.
Bake until a cake tester comes out clean—or until the top springs back when lightly pressed, 35 minutes or longer. Put the pan on the wire rack, cool briefly, then remove the side ring of the springform and let the cake cook completely.
Lift the cake off the metal pan bottom and peel off the parchment. Slice the cake horizontally in thirds, making 3 thin layers. Return the top layer of the cake to the metal pan bottom, upside down, so the crusty baked top is against the pan. This will be the base of the torta. To prepare for glazing, set the wire rack inside a rimmed baking sheet, and place the base layer on the rack.
Put 1/3 cup of the apricot preserves in a small saucepan with ¼ cup of water and heat, stirring, until the preserves dissolve into a loose syrup. Brush this syrup on all the cut surfaces of the layers, including the base, to moisten the cake.
To fill the layers, put 1 cup of thick apricot preserves in a bowl and stir just to loosen. Spread ½ cup of the filling over the base layer. Now place the center layer of the cake (the layer with two cut surfaces) on top of the base and spread the remaining apricot filling over the top. Finally, place the bottom layer of cake over the filling, upside down, so the flat, smooth surface that was originally the very bottom of the cake is now the top. Center the three layers so the sides of the torta are straight and scrape off any drippings of apricot that oozed out.
To make a thick, smooth apricot glaze to seal the cake, put the remaining 2/3 cup of apricot preserves in the small saucepan with ¼ cup of water and heat to a simmer, stirring. Pour the preserves through a small strainer set in a cup, to remove any solid bits of apricot, and immediately pour the hot strained glaze from the cup over the torta. (If you feel confident, hold the strainer over the center of the torta, and pour the glaze directly out of the pan).
Spread the glaze rapidly with an icing spatula, before it cools, coating the top completely, then spilling glaze over the edge and down the sides. Smooth the glaze against the sides to seal them. Let the apricot glaze set and scrape up any glaze that dripped on the rack or into the pan underneath.
Meanwhile, prepare the chocolate glaze. Pour the corn syrup, rum and water into a small heavy saucepan, add the pinch of salt and bring to a boil, stirring. Put the chopped chocolate in a large, heat proof bowl. Boil the syrup for a couple of minutes until slightly thickened, then pour it over the chocolate and stir until all the chunks have melted and the glaze is smooth and shiny. Let it cool, stirring occasionally, until barely warm to the touch and just starting to thicken.
Pour the chocolate glaze over the top of the torta, spreading it with a spatula so it coats the top evenly and flows over the edge and down the sides. Smooth the sides so they are evenly coated, with no bare spots. Let the glaze solidify at room temperature.
Lift the torta off the rack onto a cake plate, still on the metal disk. If you prefer, slide a broad spatula (or two) under the cake to separate it from the metal disk then lift and move. Collect any chocolate glaze that’s dripped into the pan, to use again in the future. (If you want, warm up the excess glaze and spoon it into a paper piping cone. Write the name “Sacher” across the top—the traditional inscription on Viennese sachertorte—or pipe other decorative flourishes.)
Cut in wedges to serve, with mounds of whipped cream.