This is a perennial favourite, named after the famous Viennese hotel, where you can still buy it in boxes and bring it home.
It’s dark, very chocolatey and sophisticated, and for a special occasion or a birthday, it’s nice to decorate it with sugared rose petals, see related recipe below.
This recipe is from Delia's Cakes.
Place the broken-up chocolate in a bowl over a pan containing 5cm of barely simmering water, without the bowl touching the water.
When it’s melted (5–10 minutes) take it off the heat. While that’s happening, sift the flour and baking powder into a roomy mixing bowl, lifting the sieve quite high to give the flour a good airing as it goes down.
Then add the butter, sugar, almond extract and beaten egg yolks, and, using an electric hand whisk, combine them for about 1 minute until you have a smooth creamy consistency. After that beat the chocolate into the creamed mixture.
Now, using a clean dry whisk and a large bowl, whisk the egg whites to soft peaks and then carefully and gradually fold them into the mixture bit by bit, using a metal spoon.
Pour the mixture into the prepared cake tin, level the top with the back of a tablespoon and bake it near the centre of the oven for about 40–45 minutes, or until firm, well-risen and springy in the centre. When it’s cooked, allow the cake to cool in the tin for 10 minutes before turning it out onto a cooling rack and leaving it to get quite cold.
To make the icing: melt the chocolate (as above), then remove it from the heat. Stir in the cream and the glycerine till thoroughly blended. Now warm the apricot jam and brush the cake all over with it. Finally pour the icing over the whole cake, using a palette knife to cover the top and sides completely.
Then leave it to set (which will take 2–3 hours). If you make it in advance you can store it in the fridge once the icing has set.
Serve cut in wedges – in Vienna they always serve it with a generous amount of whipped cream.
Pre-heat the oven to 150°C, gas mark 2