Preheat the oven to 190 ° C. Grease a bundt pan with butter and dust with flour. Mix butter, 250 g sugar, 1 sachet vanilla sugar and salt until frothy. Mix in the eggs one by one. Mix the flour and baking powder and stir in alternately with the whipped cream.
Halve the dough. Mix in the espresso, 1 tablespoon sugar, the second packet of vanilla sugar and the cocoa powder under half. Pour alternating light and dark dough into the pan.
Pull through in a spiral with a fork or a skewer and smooth out. Bake in the oven for about 45 minutes, if necessary cover with foil if the cake gets too dark.