Prepare the Pan: Preheat the oven to 350°F (175°C). Line the bottom and sides of a 9-inch (23 cm) springform pan with parchment paper, then set the prepared pan aside.
Cream the Butter: Place the room-temperature butter and ½ cup (100 g) of the superfine sugar in a large mixing bowl. Using an electric mixer fitted with a whisk attachment, beat on medium-high speed for about 3 minutes, until the mixture becomes pale and fluffy.
Build the Chocolate Mixture: Add the vanilla, then incorporate the egg yolks one at a time, mixing after each addition. Pour in the melted, cooled chocolate and beat for about 2 minutes, until the mixture is creamy and well combined. Set aside.
Whip the Egg Whites: In a separate large mixing bowl, beat the egg whites and salt with an electric mixer on medium-high speed for about 1 minute, until foamy. Add the remaining ½ cup (100 g) superfine sugar and continue mixing on high speed for about 5 minutes, until stiff peaks form. Fold in the Egg Whites: Add the whipped egg whites to the chocolate mixture in 3 additions. Fold gently in one direction using the same repeated movement each time. Avoid overmixing so the batter remains light and does not deflate.
Add the Flour: Fold the cake flour into the batter in 2 additions, mixing only until incorporated and no lumps remain. Keep the folding gentle; the finished batter should be light, fluffy, and silky.
Bake the Cake: Transfer the batter to the prepared springform pan and spread it evenly. Bake for about 50–60 minutes, or until a toothpick inserted into the center comes out clean. Remove from the oven and allow the cake to cool completely.
Strain the Jam: Place a mesh strainer over a medium heavy-bottomed saucepan or Dutch oven. Press the apricot jam through the strainer into the pan, removing the fruit pulp. Add the rum and cook over medium heat for 2 minutes, until the mixture is hot, smooth, and combined. Remove from the heat and set aside. Level the Cake: Once completely cool, cut a thin layer from the top of the cake to create a flat surface. Turn the cake upside down, then cut it horizontally into two layers. A cake turner can make this step easier.
Fill the Cake: Spread about two-thirds of the warm apricot jam evenly over the bottom cake layer. Place the second cake layer on top. Spread the remaining jam evenly over the top and sides, making sure the entire cake is covered.
Dry the Jam Coating: Leave the jam-covered cake uncovered at room temperature for 1 hour, or until the jam feels dry to the touch.
Melt the Glaze: Place a large heavy-bottomed saucepan or Dutch oven over low heat and add enough water to reach about 2 inches (5 cm) high. Set a large heatproof glass bowl over the saucepan, ensuring the bowl does not touch the water. Add the chopped chocolate and butter to the bowl and slowly melt for about 5 minutes, stirring frequently with a rubber spatula. Remove from the heat when the butter has completely melted and only a few small pieces of chocolate remain. Smooth the Glaze: Let the bowl rest for 5 minutes so the remaining chocolate melts completely. Stir occasionally until the glaze becomes completely smooth.
Glaze the Cake: Pour the chocolate glaze over the top of the cake all at once in a circulating motion. Immediately use a long frosting spatula to spread it across the top, allowing the glaze to flow down and cover the sides. Work quickly and use only a few movements to keep the surface smooth. A cake turner makes this easier. Set the Glaze: Leave the glazed cake at room temperature for 1 hour, allowing the chocolate coating to dry and set.
Serve the Torte: Slice the finished Sacher Torte and serve it with whipped cream.
Store the Cake: Keep the cake in an airtight container at room temperature for up to 3 days.
