Rich chocolate mousse torte

Method

1. Remove the base from a 20cm springform tin. Lightly butter inside the ring and place it upside-down, directly onto a flat serving plate. Secure it in place on each side with a small piece of Blu-Tack. Line the sides with a strip of non-stick baking paper.
2. Make the biscuit case. Put the chocolate into a heatproof bowl and add the cocoa powder and butter. Rest the bowl over a pan of barely simmering water and leave until melted, then stir until smooth. Put the digestive biscuits and sugar into a food processor and whizz, using the pulse button, to fine crumbs. Stir into the melted chocolate mixture, then tip into the lined tin and, using the back of a dessertspoon, press the crumbs firmly in an even layer over the base and at least 4cm up the sides to form a casing. Chill while you make the filling.
3. Dissolve the coffee in 4 tablespoons boiling water. Put the coffee and chocolate in a large heatproof bowl, rest it over the pan of hot water until melted and then stir until smooth. Mix the egg yolks and vanilla extract together in a small bowl. Stir into the chocolate and coffee mixture until smooth and then stir in your chosen spirit.
4. Whisk the egg whites in a bowl until just beginning to stiffen, then gradually whisk in the sugar to form a soft meringue. The tips of the peaks should fall over, not stand upright. Gently fold the whites into the chocolate mixture and then pour into the biscuit crumb case. Chill for at least 4 hours or overnight until firm before removing the springform tin.