Mix the flour, baking powder, salt, and spices in a large bowl and set aside. In another bowl, stir together the sugar and butter until frothy. Add the egg, then add the pumpkin puree. Mix thoroughly with the mixer until the mixture is light and airy. Now add this mixture to the flour mixture and finally stir in the vanilla sugar, raisins and nuts.
Grease a bundt pan and sprinkle with a little brown sugar and chopped nuts. Bake the cake for about 65 minutes. However, it is essential to do the chopstick test. Let cool in the tin, only then turn out.
Melt the couverture in a water bath, spread it on the Gugelhupf and immediately sprinkle with brown sugar and chopped walnuts.