Preheat the oven to 160°Cfan / 180c conventional / 355f. Line and grease a 20–22 cm loose-bottomed cake tin with baking parchment.
In a large bowl, beat the butter with half of the sugar (about 65 g) until light and fluffy. Add the egg yolks one at a time, scraping down the sides of the bowl as needed.
Melt the chocolate (either gently in a heatproof bowl over simmering water or in short bursts in the microwave).
Stir the melted chocolate and ground almonds into the butter mixture. The texture will look grainy - this is normal.
In a clean bowl, whisk the egg whites with a pinch of salt until soft peaks form. Gradually sprinkle in the remaining sugar while whisking until firm peaks form (before stiff peaks), but avoid whisking to the point where the egg whites look dry.
Stir about one-third of the egg whites into the chocolate mixture to loosen it.
Gently fold in the remaining egg whites with a spatula, taking care not to knock out too much air. Fold until no streaks of white remain.
Pour the mixture into the prepared tin and smooth the surface. Bake for 30–35 minutes until just set. A slightly under-baked torta caprese is far better than a dry one, so err on the side of caution.
Leave the cake to cool completely in the tin. Invert onto a plate so the bottom becomes the top, giving a smooth, flat surface. Dust generously with cocoa powder (or icing sugar, if you prefer).
The video below will help with this recipe.