Preheat oven to 350 degrees. Butter a round cake tin and set aside.
In a medium bowl, whisk together the cake flour, oat flour, baking powder and baking soda. Set aside.
In a the bowl of a standing mixer, mix the butter and caster sugar at medium speed for 3 - 5 minutes, until pale and creamy.
Scrape down the sides of the bowl and add the eggs, one at a time, mixing well between each addition.
Blend in the vanilla bean paste.
Add the flour mixture in three parts, alternating with the buttermilk, beating until just combined.
Pour the caramel sauce into the buttered cake pan. Layer the persimmon slices on top of the caramel sauce, overlapping just a bit, to the outer edge.
Spoon the batter over the persimmons and smooth the top with a spatula.
Bake for 35 - 37 minutes or until a toothpick inserted in the middle comes out clean.
Loosen the edges of the cake with a butter knife and invert the cake onto a platter while it’s still hot. Allow to cool 10 minutes before serving.