Inspired by Japanese deco rolls, Paul uses different coloured cake batters to make a patterned Swiss roll.
Equipment and preparation: You will need a piping bag fitted with a plain nozzle and a hand-held electric mixer.
Preheat the oven to 200C (180C fan)/400F/Gas 6. Grease and line a Swiss roll tin with baking parchment.
For the decorative sponge paste, cream the butter and icing sugar together until light and fluffy and then gradually add the egg whites, beating continuously. Fold in the flour then add the liquorice essence and food colouring paste and beat until the mixture is black. Spoon into a piping bag fitted with a plain piping nozzle and pipe six diagonal lines across the tin. Refrigerate the tin while you make the plain cake batter.
For the sponge, put the eggs and caster sugar into a large bowl and whisk with a hand-held electric mixer until the mixture is light and frothy and leaves a trail when the whisk is removed. Sift the flour over the mixture and carefully fold in using a large metal spoon or rubber spatula.
Gently pour the mixture into the tin, giving the tin a little shake so the mixture finds its own level; gently push the mixture into the corners if necessary. Bake for 10-12 minutes, or until the sponge is golden-brown and starting to shrink away from the sides of the tin.
Lay two sheets of parchment paper (cut a little larger than the size of the tin) on a work surface and sprinkle one with caster sugar. As soon as the sponge is cooked, turn it out onto the sheet of sugared paper and carefully peel off the lining paper. Lay the other sheet of paper over the striped top and flip over, so that the black lines are underneath. Set aside to cool.
For the filling, beat the butter, icing sugar, milk and liquorice essence in a bowl until smooth.
Once cooled, discard the sugared paper, trim the edges of the sponge with a sharp knife and score a line across the sponge 2cm/1in in from one of the short edges. Spread an even layer of the buttercream over the sponge.
Spread an even layer of jam over the buttercream. Roll up the Swiss roll firmly starting at the scored end and using the paper to help you.
