Make the brown butter sponges. Melt the butter in a pan over a medium-high heat, reduce the heat and simmer for 8–10 minutes until the butter starts to brown and smell like popcorn. Leave to cool, then chill for 1–2 hours, until set.
Heat the oven to 200°C/180°C fan/400°F/Gas 6. Beat the cooled brown butter and the sugar in a stand mixer fitted with the beater, on medium speed for 2–3 minutes, until creamy.
With the mixer on a low speed, add the eggs, one at a time, beating well between each addition. Add the flour and baking powder, until combined. Divide the mixture equally between the tins and bake for 20–25 minutes, until a skewer inserted into the centres comes out clean. Leave to cool in the tins for 5 minutes, then turn out onto a wire rack to cool completely.
Make the chocolate sponges. Re-line the tins. Beat the butter, sugar and vanilla together in a stand mixer fitted with the beater, on medium speed for 2–3 minutes, until pale and creamy. With the mixer on a low speed, add the eggs, one at a time, beating well between each addition.
Combine the cocoa powder and milk in a small bowl, then add to the batter and beat on medium speed for 30–60 seconds, until combined. With the mixer on a low speed, add the flour, until just combined. Divide the mixture equally between the tins and bake for 20–25 minutes, until a skewer inserted into the centres comes out clean. Leave to cool in the tins for 5 minutes, then turn out onto a wire rack to cool completely.
Make the buttercream. Put the chocolate and cream in a bowl set over a pan of simmering water. Stir for 2–3 minutes to a smooth ganache. Remove from the heat and leave to cool.
Beat the butter and vanilla in a stand mixer fitted with the beater, on high speed for about 1 minute, until very creamy and smooth. Add the icing sugar, one quarter at a time, beating slowly at first, then increasing the speed for 1 minute.
Slowly add the cooled ganache and beat until fluffy. Spoon one-third of the buttercream into a separate bowl and set aside.
To assemble, level the sponges. Put a dab of buttercream on a cake plate, then top with a brown-butter sponge. Cover with one-fifth of the larger portion of buttercream. Top with a chocolate sponge and spread with a fifth of the buttercream. Repeat for the second brown-butter sponge and a further fifth of the buttercream. Place the final chocolate sponge on top.
Spread another one-fifth of the buttercream around the side of the cake, and the final fifth evenly over the top. Smooth off any excess to create a crumb coat. Chill for 1 hour.
Repeat the buttercream process using two-thirds of the reserved buttercream to create a thick, even coating. (Set aside the remaining buttercream for attaching the decorations.) Chill the cake while you make the chocolate shards.
Melt the dark and white chocolates in separate bowls set over pans of simmering water. Pour the dark chocolate randomly over the lined baking tray, then pour over the white, filling any gaps. Drag the cocktail stick through to marble.
Bang the tray firmly on the work surface to get rid of any air bubbles, then leave to set. Add a gold leaf to the chocolate as it sets, if you wish. Once set, use a knife to cut it into shards.
Make the decoration. Melt the dark chocolate in a bowl set over a pan of simmering water. Remove from the heat and leave to cool for 2–3 minutes.
Pour the chocolate into the piping bag and cut a small, 5mm hole in the end. To pipe the drip, hold the bag at the top of the cake and steadily move around the edge, allowing the drips to trail down the sides, varying your squeeze to achieve different lengths. Pipe chocolate over the top of the cake, and spread it evenly with a palette knife.
Use the remaining buttercream to attach the shards, fruit and gold-sprayed cherries, as well as extra pieces of gold leaf, if you wish.