Melt crushed chocolate over a hot water bath. Occasionally stir, then leave again to cool slightly.
Separate the eggs. Beat egg whites with 1 pinch of salt until stiff.
Cut butter into pieces and stir with the sugar until foamy. Gradually add the egg yolks, then stir in the melted chocolate.
Sift flour with almonds and baking powder and mix with the nuts into the batter. Fold in the egg whites. Scrape batter onto a buttered baking sheet and smooth. Bake on center rack in a preheated oven (200°C, approximately 400°F) for approximately 25 minutes.
Remove and let cool.
To serve, cut into squares.