Method

1. Preheat the oven to fan 90C/ conventional 110C/gas 1?4 and cover a baking sheet with baking parchment. Tip the egg whites into a large bowl, sprinkle in the coffee powder and whisk until the whites are stiff. Add half the caster sugar and whisk in well, then tip in the remaining sugar and the chopped hazelnuts and whisk until blended and standing in stiff peaks.

2. Spread the meringue mixture to a depth of about 2cm on the baking parchment (any shape will do as you’re going to break it up later). Bake for 3 hours until crisp right through. Remove and cool.

3. Cut out a 28cm circle of baking parchment and make 10cm cuts towards the centre all the way round. Use this to line the bottom and sides of a loose-bottomed 20cm round cake tin.

4. Pour the cream from both cartons into a bowl and whip until it just holds its shape. Break the meringue into smallish pieces with your hands. Set aside about a third of the meringue for the top of the cake, and mix the rest into the cream. Spread out about a third of the cream mixture in the bottom of the tin and cover with half the frozen berries. Repeat these layers once more, then cover with the remaining cream mixture and top with the reserved meringue. Cover the cake with cling film and compress evenly with a small plate that fits inside the tin. Wrap in foil, label and freeze for up to a month.

5. Make the sauce. Put the cream and golden syrup in a small pan with 3 tbsp water. Heat until just bubbling, then turn the heat down to low and add the chocolate and butter. Heat gently, stirring occasionally, until the chocolate melts and the mixture becomes smooth and glossy. Pour into a freezer container, cool, seal, label and freeze for up to a month.

6. On the day transfer the cake and the chocolate sauce from the freezer to the fridge 8 hours before you plan to serve. After 2-3 hours, take out the cake. Unwrap it and carefully balance the cake tin on a jam jar or can, then push down on the sides of the tin to release. Peel away the baking parchment from the sides. Now lift the cake off the base of the tin, discarding the parchment underneath (a wide palette knife or fish slice will help here) and stand the cake on a serving plate. Return to the fridge for 5 hours before serving with the chocolate sauce.

7. To warm the chocolate sauce, pour it into a heatproof bowl over a pan with a little hot water in the bottom and heat gently, stirring occasionally, until warm, smooth and glossy.