Preheat the oven to 375 degrees F (190 degrees C) with a rack in the center of the oven. Butter and flour the sides of a 9-inch springform pan, then line the bottom with a circle of parchment paper.
Bittersweet Chocolate (3/4 cup)
in a heat-proof bowl and heat over a small saucepan of barely simmering water or in the microwave until just melted. Set aside and cool completely while stirring often.
Unsalted Butter (1/2 cup)
in a large mixing bowl and beat on medium speed until very light and creamy. Add the
Powdered Confectioners Sugar (1 cup)
on low speed then increase to medium speed and beat again until light and creamy.
Beat in the
Egg Yolks (6)
, one at a time, scraping down the sides of the bowl.
Add the cooled chocolate and
Vanilla Extract (1 tsp)
and beat until well-mixed and very light and creamy, scraping down the sides of the bowl.
In a clean bowl, beat the egg whites with about 1 Tbsp of the
Granulated Sugar (1/2 cup)
on high speed until foamy. Gradually add in the rest of the sugar and continue beating the whites until they form soft, shiny peaks – they should hold their shape but flop over on themselves.
Vigorously stir about 1/3 of the whipped egg whites into the chocolate mixture to lighten it, then gently fold the remaining egg whites into the chocolate mixture with a spatula until just a few wisps of egg white remain. Do this carefully so as not to deflate the egg whites.
Stir together the
All-Purpose Flour (1 cup)
Fine Sea Salt (1 pinch)
and sift half of it over the chocolate mixture. Fold in with a spatula until almost incorporated. Sift the remaining flour and fold to combine completely.
In a prepared springform pan, spread the batter evenly and bake for 35-45 minutes or until a toothpick comes out clean. Meanwhile, make the apricot glazing.
To make the apricot glaze, boil the
Apricot Jam (1 1/4 cups)
Water (2 Tbsp)
in a small saucepan over medium heat. Cook and stir until the mixture thickens about 2-3 minutes. Strain through a wire mesh sieve and keep warm until ready to use.
Cool the cake in the pan for 10 minutes, then run a knife around the edge to loosen it from the pan and remove the sides. Carefully invert the cake onto a rack and remove the bottom of the pan and parchment paper, then turn the cake right-side-up onto a rack and allow it to cool completely.
Turn the cake upside-down so that the flat side is on top. Cut the cake horizontally into two even layers.
Place one cake layer on the 8 1/2-inch cardboard cake round and spread it generously with about half of the apricot glaze. Allow it to soak in.
Place the second cake layer on top and spread the top and sides with the remaining apricot glaze. Work quickly before the glaze has a chance to set and use a metal offset spatula to smooth the top. Allow the apricot glaze to set once it's smooth.
To make the chocolate glaze, place the
Granulated Sugar (1 cup)
Water (1/2 cup)
in a heavy-bottomed saucepan over medium-high heat and bring to a boil, stirring occasionally.
Attach a candy thermometer and cook, stirring, until the mixture reaches 234 degrees F or 112 degrees C, about 5 minutes. Remove the saucepan from the heat and whisk in the
Bittersweet Chocolate (1 cup)
. If it thickens, return it to low heat and add few drops of water if necessary.
This glaze should be smooth and shiny. Turn off heat and stir the glaze for 30-60 seconds to cool it slightly, then immediately use it to glaze the cake.
Pour the chocolate glaze over the top of the cake, first around the edges, then in the middle. Spread the excess glaze over any bare spots using a metal offset spatula. Before the glaze has a chance to set, move the cake to a serving platter.
To make the writing chocolate, heat
Bittersweet Chocolate (1/4 cup)
until just melted and stir in
Vegetable Oil (1/2 tsp)
to get a pipeable consistency. Let the mixture cool down a little if it's too runny. Place the mixture into a disposable piping bag.
With the writing chocolate, pipe the word "Sacher" in the middle of the cake and add any decorative flourishes you wish. Chill the cake until the glaze is completely set, at least 1 hour.
To serve, let the cake come to room temperature for about one hour before serving. Whip the
Heavy Cream (1 cup)
to soft peaks.
Cut the Sachertorte into wedges with a large sharp knife dipped in hot water and wipe off the blade between cuts. Serve each slice with a dollop of whipped cream.