Method

1. Heat the oven to 180C/160C fan/gas 4 and lightly oil a 33 x 23cm swiss roll tin. Line the base and sides with baking parchment, then lightly oil again. Melt the dark chocolate in a heatproof bowl set over a pan of simmering water (ensuring the base of the bowl doesn't touch the water), or in 20-second bursts in the microwave. Set aside to cool slightly.

2. Separate the eggs, putting the whites in one large bowl and the yolks in another. Whisk the whites to stiff peaks using an electric whisk – they should hold their shape. Tip the sugar into the yolks and whisk until the mixture is pale. Fold the melted dark chocolate into the yolk mixture, then loosen the chocolate mixture by folding in two big spoonfuls of the whipped egg whites. Add the remaining whipped egg whites, cocoa and ¼ tsp salt, and gently fold everything together to combine, being careful not to knock out the air. Spoon the batter into the prepared tin and bake for 18 mins. Remove from the oven and leave to cool until warm.

3. While the sponge is still warm, gently roll it up into a spiral (with the baking parchment inside) from one of the short ends. Leave to cool completely, still rolled up (this will make it easier to roll once it's been filled). Melt the white chocolate as you did the dark, then leave to cool for 10 mins. Whisk together the vanilla, mascarpone, double cream and melted white chocolate until the mixture is thick and spoonable. 

4. Place the rolled-up roulade on a sheet of baking parchment and carefully unravel. Remove the original baking parchment, then evenly spread the mascarpone and white chocolate filling over the sponge, leaving a small border around the edges. Using the parchment to guide you, roll the roulade back into a spiral and chill for 20 mins. 

5. For the topping, heat the double cream in a small pan over a low heat until steaming. Tip the milk chocolate into a heatproof bowl with the golden syrup, then pour over the hot cream. Leave to stand for a moment, then stir everything together until melted together and smooth. Sit the roulade on a wire rack set over a baking tray and gently spoon the ganache over the top so it drips down the sides. Top the roulade with the mini chocolate eggs and pieces of chocolate, then leave to set slightly before cutting into slices. Will keep covered and chilled for up to 24 hrs.