Wash the pumpkin, chop it and boil it in some water until soft. Check the water again and again, not that the pumpkin is burning. Puree the pumpkin.
Mix the butter with the sugar until frothy. Stir in the cinnamon and cocoa. Then add the eggs and buttermilk and the pumpkin. Also stir in flour and baking powder or fold in sifted.
Bake the dough in a 24 or 26 cm springform pan at 180 ° C top and bottom heat for about 35 minutes. Do a chopstick test.