Preheat oven to 350 degrees F.

Peel persimmons and chop into chunks. Transfer to a high speed blender or food processor and process until smooth and fully blended (note- I did not strain through a mesh strainer).

Place the persimmon pulp, pumpkin puree and sugar into a large mixing bowl. Mix well. Beat the eggs in with the persimmon mixture.

In a seperate, smaller bowl, whisk together the buttermilk and the baking soda. Transfer to the persimmon mixture and stir to combine.

In a separate mixing bowl sift together the flour, baking powder, cinnamon and salt. Slowly add to the persimmon pumpkin batter and stir well to combine. Add the heavy cream and mix well.

Grease a 9" x 13" baking dish with the butter. Stir any remain butter in with the batter.

Pour the batter into prepared baking dish and bake until toothpick inserted into the center comes out clean (approximately 50 minutes to 1 hour).

Set aside to cool and serve with whipped cream, if desired.