Step 1

Preheat the oven to 350°F. Line the bottom of two 9 inch cake pan with parchment paper, or butter and flour the bottom of the pans. You don't need to butter/flour the sides of the pans.

Step 2

Sift together the flour, baking powder and salt, set aside.

Step 3

Cream the butter and 3/4 cup of the granulated sugar until light and aerated. Add the egg yolks and vanilla, mix until combined. Mix in the sifted dry ingredients, don't over mix. Whisk the white chocolate into the batter.

Step 4

Whip the egg whites to soft peak. Slowly add the remaining 1/4 cup of sugar and whip to full peak. Fold the egg whites into the batter in 3rds, mixing until there are no streaks of egg white visible.

Step 5

Divide the batter between the prepared pans and bake until the middle of the cake springs back when pressed or a toothpick inserted into the middle comes out clean, about 20-25 minutes.

Step 6

Cool the cakes for 10 minutes in the pan then turn out onto a cooling rack until completely cooled (see note).

Step 7

Stir the rum into the apricot preserves.

Step 8

Using a serrated knife trim the top of the cakes so they are flat. Place one layer onto a cardboard cake round (it makes handling the cake easier). Spread 3/4 of the apricot mixture onto the bottom layer and place the other layer onto the cake.

Step 9

Strain the remaining apricot preserves into a clean bowl to remove the chunky bits of fruit. Ice the top and sides of the cake with the remaining apricot preserves. Place the cake in the freezer for at least 30 minutes while you make the glaze.

Step 10

Microwave the white chocolate in 15 second increments until melted. In a separate bowl, melt the butter with the hot water and corn syrup. Stir the warm butter mixture into the melted white chocolate until it's smooth.

Step 11

Remove the cake from the freezer and set it on a cooling rack set over a clean sheet pan. (If you are using a cardboard cake circle trim the excess so the board is the same size as the cake.) Starting at the center of the cake, pour the glaze all at once over the cold cake. Use a small spatula to spread the glaze over the top and let it fall over the sides of the cake. Use the spatula to fill in any gaps on the sides. You must work quickly before the glaze begins to set.

Step 12

For the traditional design, pipe the word "Sacher" onto the cake using melted white chocolate. Use a potato peeler to make shavings from a bar of white chocolate. Sprinkle the shavings around the top edge of the cake. Allow the glaze to set completely before moving the cake to a serving platter.

Step 13

Store and serve at room temperature. The assembled cake will improve for a day or two after being iced as the apricot preserves absorb into the cake.