To make the praline, lightly grease and line a baking tray. Place the sugar in a saucepan and stir over medium heat until it starts to melt.
Continue stirring until it dissolves and begins to turn a pale golden colour. Watch it carefully as it becomes clear. When it turns a golden caramel colour, stir in the roasted almonds and mix to coat them.
Pour the mixture onto your prepared baking tray and flatten out with a spoon - be careful, it is very hot! Allow to cool, then roughly chop. This will keep for a few weeks in an airtight container.
To make the truffle cake, line a 23cm x 12cm loaf tin with baking paper. Place praline in a plastic bag and crush with a heavy rolling pin.
Melt the chocolate in a bowl over a saucepan of simmering water.
Beat butter until pale and fluffy, then add the melted chocolate and rum. Stir to combine.
Whip cream until soft peaks form, taking care not to overbeat and stiffen it. Fold chocolate mixture into the whipped cream until combined, then gently fold through the crushed praline. Pour mixture into your prepared loaf tin and leave to set in the freezer for 3-4 hours or overnight.
An hour before serving, transfer cake to fridge to gently soften. Unmould the cake onto a serving dish and serve slices with berry coulis.