Break the chocolate into pieces and melt in a hot water bath while stirring. Let it cool down. Preheat the oven (electric cooker: 160 °C/circulating air: 140 °C/gas: see manufacturer). Grease a springform pan (26 cm Ø).
Cream 400 g butter and sugar with the whisk of the mixer. Stir in the eggs one by one.
Mix flour and baking powder and stir in slowly. Finally, stir in liquid chocolate. Smooth the dough in the mould. Bake in a hot oven for 45-55 minutes. Let it cool down. Whipped cream tastes good with it.