1. For the brittle, heat the grill on the oven and line a baking tray with grease-proof paper.
2. Put 4 small mounds of sugar, evenly spaced, on the baking tray. Scatter the pine nuts on top. Melt and caramelise under the grill until golden yellow. Take out from under the grill immediately; remove from the tray, still on the paper, and leave to cool.
3. For the base of the cakes, finely grind the biscuits in a food processor and mix with the butter. Knead to form a dough. Roll out between two sheets of cling film and cut out circles of approx. 7-8 cm in diameter. Place on a baking tray or flat plate, cover and chill in the fridge.
4. For the mousse, melt the chocolate in a small heatproof bowl over a bain marie. Remove from the heat and allow to cool slightly.
5. In a medium bowl, beat the egg yolks, sugar, rum, and a pinch each of cinnamon, cardamom and cloves over a bain marie until thick and creamy. Pour in the chocolate, stirring constantly. Remove from the bain marie and beat until cold (over a bowl of cold water if necessary).
6. Whisk the egg whites with a pinch of salt until stiff, then fold into the egg yolk mixture. Likewise, whip the cream until stiff and fold through the mixture.
7. Line a second baking tray with grease-proof paper and place four ring moulds (7-8 cm in diameter) on the tray. Moisten the edges and line with strips of grease-proof paper. Spoon the mousse into the rings, smooth the tops flat, place the torte bases on top and chill for at least 3 hours in the refrigerator.
8. Before serving, turn out onto plates and remove the paper. Garnish with the brittle and serve.