To make the chocolate shards, heat the chocolate in a heatproof bowl over a pan of barely simmering water until melted. Pour evenly onto a lined baking tray to about 30 x 20cm, then tap the tray on the worktop to smooth. Scatter with 1 tbsp galaxy sprinkles; transfer to the fridge for 10 mins or until just set. Using a sharp knife, and score lines to create different shard shapes – will make it easier to cut distinct shards later. Transfer to the fridge to set fully while you bake the cake.

Preheat the oven to gas 4, 180°C, fan 160°C. Grease and line 3 x 20cm cake tins with baking paper. Put the cocoa in a heatproof bowl and whisk in 200ml boiling water until smooth. Leave to cool for 10 mins.

Beat together the butter and sugar with an electric whisk for 5 mins or until light and fluffy. Add the eggs, one by one, whisking after each addition. If the mixture starts to split, stir in 1 tbsp flour before adding the next egg. Add the vanilla, oil, and cooled cocoa mixture and beat for 1 min until well combined.

Sift over the flour and baking powder and fold in gently until just combined. Divide evenly among the tins and bake for 20 mins until a skewer inserted in the center comes out clean. Leave to cool in the tins for 10 mins, then transfer to a wire rack to cool completely.

Meanwhile, make the salted caramel. Gently heat the sugar, syrup, and butter in a pan, stirring occasionally, until everything has melted together. When it starts to bubble, stir in the cream and simmer gently for 2 mins. Stir in the sea salt, then remove from the heat to cool completely and thicken.

For the buttercream, beat the butter with an electric whisk for 2-3 mins until smooth and pale. Sift the icing sugar into a large bowl, then add 1 heaped tbsp at a time, beating all the time, until combined. Continue to beat for 5 mins until pale and aerated. Add 100g of the cooled salted caramel, then beat for a further 1 min until smooth.

Sandwich the sponges together with some of the buttercream, then cover the top and sides with it, spreading evenly with a palette knife. Transfer to the fridge to set for 1 hr.

Carefully pipe the chocolate drip icing onto the cake, squeezing pea-size amounts onto the edge to drip down the sides. Be careful not to touch the drips while they dry.

While the drips are setting, break the cold melted chocolate into shards. Make incisions at the top of the cake, then secure the shards in them. Scatter the remaining galaxy sprinkles around the shards. The cake will keep in an airtight container for up to