Preheat the oven to 350 degrees F (175 degrees C). Grease and flour a 9-inch round cake pan.
In a medium bowl, mix together the flour, baking powder, baking soda, and salt. Set aside.
In a large bowl, cream together the butter and brown sugar until light and fluffy. Beat in the eggs one at a time, then stir in the vanilla. Beat in the flour mixture alternately with the buttermilk, mixing just until incorporated.
Spread the batter in the prepared pan. Arrange the persimmon slices and walnuts over the batter. Bake for 40 to 45 minutes, or until a toothpick inserted into the center of the cake comes out clean.
Let the cake cool in the pan for at least 10 minutes before inverting onto a plate. Serve the cake warm with a dollop of whipped cream, if desired.
Interesting Facts
Persimmon is a fruit that is native to East Asia.
The persimmon is a symbol of fertility and abundance in some cultures.
Persimmons are high in vitamins A and C, which are important for a healthy immune system.
Persimmons are high in sugar and carbohydrates, so they should be consumed in moderation.