Step 1

Preheat the oven to 200°C.

Step 2

Cube the sweetpotatoes and boil in water for about 10 minutes, or until tender. Drain well and blend into a smooth purée. Set aside to cool.

Step 3

Grease and line a baking tray with parchment paper.

Step 4

In a large bowl, whisk the eggs and sugar using a stand mixer on high speed for about 5 minutes, until the mixture is pale and doubled in size.

Step 5

Sift the flour and cocoa powder, then add the vanilla extract and sweetpotato purée. Gently fold into the egg mixture until no pockets of flour remain, taking care not to deflate the batter.

Step 6

Spread the mixture evenly over the prepared baking tray and bake for about 10 minutes, until well risen and springy to the touch.

Step 7

While still warm, turn the sponge out onto a chopping board and carefully remove the parchment paper.

Step 8

For the vanilla filling, whip the double cream, mascarpone, icing sugar and vanilla extract together in a stand mixer until soft peaks form.

Step 9

Spread the cream filling evenly over the sponge, then roll tightly from one short end to form a log. Transfer to a serving plate.

Step 10

Use the remaining cream to cover the outside of the log. Create bark-like texture using the prongs of a fork for a festive look.

Step 11

For the sweetpotato icing, boil and mash the sweetpotatoes until smooth, then mix with icing sugar until fully combined.

Step 12

Spoon or pipe the icing over the log and decorate with festive toppings before serving.