For the coconut oat cake, add eggs, sugar, buttermilk, flour, baking powder and cinnamon to a food processor and mix to a dough.
Preheat the oven to 140 °C, line a baking tray with baking paper and spread the batter evenly on it.
For the topping, mix coconut flakes with sugar and spread on the cake. Bake for half an hour. Meanwhile, heat flour, whipped cream and rum together in a pot.
Immediately after the baking time, pour the whipped cream over the cake and let it cool.