Preheat oven to 350°F. Grease and flour a 9-inch cake pan.
In a large bowl, mix together persimmon puree, brown sugar, and oil. Whisk in eggs and vanilla.
In another bowl, combine flour, cocoa powder, baking powder, cardamom, and salt. Stir into wet ingredients until just incorporated. Fold in chopped chocolate.
Pour batter into prepared pan.
Bake for 25 minutes. Let cool slightly in pan, then turn out onto a rack to cool completely.
Notes
If using mini bundt molds, reduce cooking time to 20 minutes.