For the Sacher cake, cream the butter and add the sugar by the spoonful, mixing well. Melt the chocolate in a bain-marie and allow to cool, add to the butter-sugar mixture.
Beat in the eggs one at a time, then stir in the flour mixed with baking powder and cornflour. Line a 26 cm springform pan with parchment paper, pour in the batter and bake for 55-65 minutes at about 150 °C.