Heat the oven to 350°F. Coat a 10-cup (2.5-liter) Bundt cake or tube pan with butter or nonstick cooking spray.
In a large bowl, whisk together the flours, baking soda, cinnamon, salt, and nutmeg. Stir in the brown sugar. In a medium bowl, whisk together the melted butter, persimmon purée, yogurt, eggs, whiskey, and vanilla.
Make a well in the center of the flour mixture, add the persimmon mixture, and gently stir. Fold in and the nuts if using. Mix just until everything is moistened; don’t overmix.
Scrape the batter into the prepared pan and bake until a toothpick inserted into the cake comes out clean, about 1 hour. Remove from the oven and let cool completely. Once cool, invert the cake onto a serving plate.
Leftovers will keep, well-wrapped, in the fridge for up to one week.