Step 1: Preheat the Oven and Prepare the Tin

1. Preheat the oven to 180°C (350°F) and grease a 23cm springform cake tin. Line the bottom with baking parchment.

Step 2: Melt the Chocolate and Butter

1. In a heatproof bowl, melt the chocolate and butter together over a pan of simmering water. Stir until smooth and well combined, then remove from the heat and let it cool slightly.

Step 3: Separate the Eggs

1. Separate the eggs, placing the yolks in one bowl and the whites in another. Add the sugar to the egg yolks and whisk until pale and creamy.
2. Stir the Amaretto liqueur, ground almonds, and vanilla extract into the egg yolk mixture, then fold in the melted chocolate and butter mixture.

Step 4: Whisk the Egg Whites

1. Using an electric hand mixer, whisk the egg whites until stiff peaks form. Be sure not to over-whisk, as this can make the whites dry.

Step 5: Fold in the Egg Whites

1. Gently fold the whisked egg whites into the chocolate mixture, a little at a time, ensuring the batter stays light and airy.

Step 6: Bake the Cake

1. Pour the batter into the prepared cake tin and smooth the top with a spatula. Bake for 35-40 minutes, or until the cake is firm around the edges and slightly soft in the center.
2. Let the cake cool in the tin for 10 minutes before transferring it to a wire rack to cool completely.