1. Preheat the oven to 180°C (350°F).
2. Cream the softened butter and sugar together for 3 minutes in the bowl of a stand mixer fitted with the paddle attachment, or by hand using a wooden spoon. Then add the almond powder, mix well, and gradually incorporate the eggs one by one. Mix until the sugar is dissolved.
3. Sift the flour, then gradually incorporate it into the mixture until you have a smooth and homogeneous batter.
4. Grease and flour a 25 cm (10 inch) round cake pan, pour in the batter, and bake for 35 to 40 minutes.
5. Let the cake cool for a few minutes, then remove it from the pan. Immediately brush the top with 4 cl (1.35 fl oz) of rum to soak it. Let it cool completely.
6. Mix the powdered sugar, the remaining rum, and a little water: you should obtain a smooth glaze that is not too liquid; if necessary, add more powdered sugar. Spread it over the top of the cake. Let it harden.