1. Grease and line a deep, 18cm loose-bottomed cake tin with a double layer of clingfilm. Melt the chocolate and butter in a bowl set over a pan of simmering water, then remove from the heat and stir through the golden syrup. Put the broken biscuits in a large bowl and fold in the chocolate mix to coat. Transfer to the tin, pressing the top gently with a potato masher to level. Chill for 3-4 hrs to set.
2. Meanwhile, draw a 12 x 30cm rectangle on a sheet of baking paper, then make 4 more lines along the long side, measuring 6cm between each, to give 5 thinner rectangles. Mark a line halfway along the short side: from here, draw the top of the rectangles down to sharp points. Repeat with a second sheet of baking paper, then use to line 2 baking sheets, pen-side down.
3. Melt 75g white chocolate in a bowl set over a pan of simmering water. Set aside for 5 mins to cool slightly, then spoon into a disposable piping bag and snip a 4mm hole. Pipe the outlines of the jagged rectangles marked out on the baking paper, then transfer to the fridge for a few mins.
4. Melt the remaining 125g white chocolate as above, then spoon into the piped outlines, using a teaspoon to nudge into the corners. Tap the sheet on the worktop to level the surface, then transfer to the fridge for 20 mins.
5. Dip a large knife in hot water, wipe dry, then gently press between the points to create 10 shards with pointed tops. Lightly spray with gold shimmer spray, then return to the fridge to dry. Once dry, repeat with another layer of gold spray; repeat to build up a strong gold colour.
6. Use the gold decorating icing to pipe dots and crosses onto the chocolate shards, sticking a blueberry into the centre of each cross. Return to the fridge to set until needed.
7. For the ganache, heat the cream in a saucepan until steaming and just beginning to bubble at the edges. Put the dark chocolate in a heatproof bowl; pour over the warm cream. Stir briefly, then set aside for 5 mins. Stir again to make a glossy ganache. Leave for another 5 mins to thicken slightly.
8.Invert the biscuit cake so the smoothest side is facing upwards, then place on a wire rack set over a baking tray lined with clingfilm. Pour the ganache over the cake, allowing it to drip down the sides. Use a palette knife to spread the ganache evenly around the sides so they’re well coated. Leave to set for 15 mins, then carefully transfer to a cake board or plate (it will still be a little wet). Press the gold chocolate shards onto the sides.
9. For the decoration, spray the top of the cake and inside of the shards with gold. Use a little of the decorating icing to stick the gold pearls around the bottom edge of the shards, then decorate the top of the cake with the remaining berries. Transfer to the fridge for 1 hr, or until needed. Will keep in an airtight container in the fridge for 3-5 days.
Cook's Tip: You can also use this decoration on a ready-made 18cm cake. For the shards, measure the height of the cake and match the short side of your rectangles to this height.
Freezing and defrosting guidelines
In order to enjoy optimum flavour and quality, frozen items are best used within 3 months of their freezing date. For more tips on freezing and defrosting food, read our article Love Your Freezer.
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