Grease a 7cm-high, 24cm (base measurement) springform pan and line the base of the pan with a 7cm-wide strip of baking paper.

In a small bowl set over a small saucepan of simmering water (don't let the bowl touch the water), add 40g of the dark chocolate and the butter and stir until melted and blended.

In a food processor, process the biscuits into very fine crumbs. Add the chocolate mixture and a pinch of salt and pulse until mixture comes together. Press evenly over the base of the prepared pan. Place in the fridge to chill.

In a small microwave-safe bowl, sprinkle gelatine powder over 2 tbs cold water. Set aside for 2 mins to soak or until gelatine softens. Microwave on high (100%) for 20 seconds. Whisk until gelatine dissolves.

Place remaining 70% dark chocolate in a medium heatproof bowl. In a small saucepan over medium heat, bring ¼ cup (60ml) cream to a simmer. Remove from heat and stir in gelatine mixture. Pour over the chocolate and whisk until smooth. Set aside for 10 mins to cool or until mixture is at room temperature.

In a clean medium bowl, use an electric mixer to whisk 1 ½ cups (375ml) cream with the icing sugar until soft peaks form. Fold one-third of the whipped cream through the cooled chocolate mixture until blended and light in colour. Gently fold in remaining whipped cream until mousse is blended.

Evenly spread half the mousse over the chilled crust in the prepared pan. Sprinkle half the raspberries over the mousse. Top with remaining mousse and gently spread to create an even layer. Place in the fridge for 4 hours to chill or until mousse is set and firm.

In a small saucepan, bring remaining cream to a simmer. Remove from heat and add the dark chocolate. Stir until smooth. Set the ganache aside for 5 mins to cool or until lukewarm.

Pour the ganache over the mousse and smooth the surface. Return to the fridge for 30 mins to chill or until ganache has softly set.

Transfer the cake to a large serving plate. Top with the strawberries and remaining raspberries. Cut cake into wedges to serve.