Preheat the oven to 350°F.
Butter a 9-by-13-inch baking pan.
Cut the persimmons in half crosswise and use a spoon to scoop out the flesh, discarding the stem and skins.
Use the back of a spoon to press the flesh into a soft pulp.
Measure 2 cups (freeze the rest or reserve for another use).
Combine the pulp, sugar, egg's, and vanilla in a medium bowl.
In a large mixing bowl, sift together the flour, baking soda, baking powder, salt, and cinnamon.
Add the persimmon mixture, one third at a time, beating well after each addition.
Stir in the buttermilk, cream, and melted butter.
Pour into the prepared pan and bake until nicely browned and slightly puffed at the edges, about 45 minutes.