Method

• 1.
  For the mousse, melt the chocolate in a heatproof bowl set above a saucepan of simmering water (don’t let base of bowl touch the water), stirring occasionally, until smooth. Stir in one-third (150ml) of the cream until thoroughly combined then set aside for 5-10 minutes to cool down slightly (see recipe notes). Whisk the remaining 300ml cream and the sugar until firm peaks form. Stir whisked cream through the chocolate mixture in two batches until combined.
• 2.
  Combine the espresso and Marsala in a shallow bowl. Dip 6 biscuits, one at a time, in coffee mixture and arrange in a single layer in the base of a 23cm x 10cm (base), 7cm-high loaf pan to cover the entire base.
• 3.
  Dollop over half the chocolate mousse and level surface with a spatula. Cover with remaining biscuits, dipping them one at a time in the coffee mixture. Cover with remaining mousse and level surface with a spatula.
• 4.
  For the ganache, place the chocolate in a heatproof bowl. Bring the cream almost to the boil in a small saucepan over medium heat. Pour over the chocolate and stand for 5 minutes, then stir until melted and fully combined. Stand to cool slightly and thicken (you want it to thicken but still be pourable). Pour over mousse to fully cover. Chill, uncovered, overnight.
• 5.
  Bring to room temperature to serve.