Grease and line with parchment paper, the base and sides of a 20 cm (8-inch) springform tin or cake pan with removable base. Preheat the oven to 180°C (350°F).
Add the chocolate and butter into a heatproof bowl set over a saucepan of simmering water, ensuring the base doesn’t touch the water. Stirring occasionally, heat until the chocolate and butter have melted completely. Remove from the heat, stir in the Amaretto and set aside to cool slightly.
Meanwhile, separate the egg yolks from the egg whites. In the bowl of a stand mixer fitted with the whisk attachment, add in the egg yolks and half of the sugar and beat on medium to high speed until thick and pale, and the mixture forms a ribbon when the whisk is lifted. (Alternatively, use electric hand-held beaters.)
Into the melted chocolate, add in the ground almonds, cocoa powder and salt and mix to combine.
In a bowl of a stand mixer fitted with a clean and dry whisk attachment, add in the egg whites and whip on medium until soft peaks form. With the whisk still running, add in the sugar slowly and whip until stiff peaks form.
Spoon ¼ of the meringue mixture into the chocolate almond batter and fold through. Add in the remaining meringue and fold through gently until fully combined, ensuring that you don't knock out the air.
Pour the batter into the prepared pan and level with an offset spatular. Bake for 25-30 minutes until a toothpick inserted into the centre comes out with a few crumbs still attached to it. Remove from the oven and set on a wire rack to cool until slightly warm or completely cool before releasing the cake from the tin and setting it on your serving plate— dust with cocoa powder to serve.