1. Preheat the oven to 350°F (180°C). Butter the bottom and sides of a 9 inch cake pan.
2. In a large mixing bowl use a wooden spoon to beat the softened butter with the sugar until light and fluffy. Beat in the ground almonds and vanilla, then beat in the eggs, one at a time. Finally stir in the flour, just until the batter is completely blended.
3. Pour and scrape the batter evenly into the prepared pan. Place the pan in the preheated oven and bake for 40 minutes or until cooked through in the center.
4. Remove the cake from the oven and allow to cool for just five minutes before turning it out onto a wire rack. Immediately pour the 1/4 cup of rum evenly over the top. Allow the cake to cool completely before icing.
5. To make the icing, mix the remaining 2 tablespoons of rum with 1 tablespoon of water and 1 cup of powdered sugar. Pour the icing onto the cooled cake and spread it evenly over the top, allowing some to icing to spread down the sides.
6. Refrigerate the cake until the icing firms up, then wrap loosely in plastic wrap and continue refrigerating. This cake gets better as it sits, so it can be made a day ahead if you wish.

Makes 12 dainty (yet powerful) slices.