Melt the butter with the chocolate in a small saucepan. Finely chop the almonds in a food processor.

Separate the egg yolks from the whites. Beat the egg whites with two tablespoons of sugar until stiff peaks form. In a separate bowl, beat the yolks with the remaining sugar and the rum until the mixture is pale and fluffy.

Add the melted chocolate to the yolk mixture and continue beating. Stir in the chopped almonds, and once combined, gently fold in the beaten egg whites a little at a time using a spatula, being careful not to deflate the batter.

Grease a 8-inch (20 cm) cake pan very well and pour in all the batter. Bake at 350°F (180°C) for 25–30 minutes, until a thin crust forms on top but the inside remains soft.

Remove from the oven and let cool completely before taking it out of the pan. Dust with powdered sugar before serving.