1- Preheat the oven to 175 C (350 F).
2- Butter a cake pan and sugar it. Place 1 tablespoon of sugar at the bottom of the buttered pan and, by turning the pan on its sides, make the sugar adhere to the walls.
3- In a large bowl, mix the flour, almonds, eggs, baking powder, sugar, vanilla, and melted butter, using a whisk. Add the milk and mix well. Pour the batter into the sugared pan.
4- Add the plum halves to the batter.
5- Bake for about 20 minutes or until a wooden pick inserted into the cake comes out almost dry.
6- Serve warm or at room temperature.