Sacher torte

Put the butter and sugar in a bowl and beat until the mixture is light and fluffy. Beat in the chocolate and vanilla extract, then the egg yolks one at a time. Fold in the plain flour. Whisk the egg whites until stiff. Fold into the chocolate mixture, then pour the mixture into a 23cm (9in) round cake tin, lined with baking parchment. Bake in the oven for 45-60 mins at 170C (325F, gas mark 3) or until the cake feels firm to the touch in the centre and a skewer comes out clean after being inserted into the middle. Remove from the oven and leave to cool in the tin, then transfer the cake to a wire rack. To make the ganache, bring the cream to the boil, then pour it over the chocolate and stir in the liquid glucose. Leave to cool, stirring occasionally, until it's a coating consistency. Slice the cake in half horizontally. Spread one half with apricot glaze or jam, then put the two pieces back together. Spread the remaining glaze or jam over the top and sides of the cake. Place the cake on a wire rack over a plate or tray. Pour the ganache over the top, using a palette knife to spread it evenly. Any ganache that runs off can be reused. Leave the cake in a cool place until the ganache has set, then use a long knife to mark the cake into 8 or 10 portions. Fill a small disposable piping bag with the cake covering and cut off the end of the bag to give a small hole. Pipe the word 'Sacher' on each slice. Leave to set before serving.