Soak Dried Pitted Prunes (100 gram) in Rum (3 1/2 tablespoon) and Caster Sugar (1 tablespoon) for about an hour. Then simmer prunes over low heat for about 5 minutes until prunes swelled. Remove from heat and leave to cool. Reserve 6 pieces pitted prunes for topping and cut the remaining pitted prunes into small pieces.
Line a 7 inch round cake pan with parchment paper at the bottom and grease the sides. Preheat oven to 190 degrees C (375 degrees F).
Cream Butter (150 gram) and Caster Sugar (125 gram) at medium speed until light and fluffy, about 5 minutes.
Gradually add beaten Large Egg (3) little by little, combine the egg mixture well after each addition. Add Lemon Juice (1 tablespoon), Vanilla Extract (1 teaspoon) and Rum (2 tablespoon) and mix well again.
Sift the Cake Flour (170 gram) and Baking Powder (1 teaspoon) the second time directly to the egg mixture and gently fold well with a rubber spatula. Then add Milk (2 teaspoon) into it and fold the batter to smooth. Throw in the prunes pieces and fold evenly.
Pour batter into prepared cake pan, smooth the top and place whole pitted prunes over it. Bake in preheated oven at 190 degrees C (375 degrees F) for 10 minutes.
Then reduce temperature to 170 degrees C (340 degrees F) and bake for another 30-40 minutes or skewer inserted into the center of the cake comes out clean.
Leave cake to cool in pan for 10 minutes. Then remove cake and place on wire rack to cool.