For the coffee caramel, combine the caster sugar and ¼ cup water in a saucepan, bring to a boil, then simmer until the sugar forms a dark caramel. Stir in the brown sugar, espresso and 150ml cream and simmer for just a minute, stirring constantly until the caramel is dissolved. Set aside to cool to room temperature, then place in the fridge to thicken.

Combine 450ml cream, mascarpone and sugar in a bowl and whip to soft peaks. The mixture should not be too stiff. Place the coffee and brandy (or rum) in a deep tray and dip half the savoiardi biscuits into this coffee mixture until softened but not falling apart. Arrange these biscuits in the base of a 24cm square serving dish. Cover with a thick layer of the cream mixture, ensuring there are no air pockets. Repeat with another layer of soaked biscuits, laying the biscuits in the same direction as the first layer, and a final thick layer of cream. Tap the dish against the bench to flatten the top and remove any air pockets.

Add a few dollops of the coffee caramel to the top of the dish. Then, using a skewer, swirl the caramel into the cream mixture to create a pattern. Refrigerate for at least 3 hours before serving. Serve with the remaining coffee caramel.