Start with the mixture for the pattern
Separate one egg and weigh the white of it
Mix together the same weight of icing sugar and butter.
Add the egg white to the mixture and combine well
Then add the same weight of plain flour and mix well
Add green food colouring until it reaches the shade you want
Put the mixture into a piping bag and snip the end of the bag off with some scissors
Onto a lined baking tray, pipe diagonal lines, or a pattern of your choice
Put the tray into the freezer for one hour
To make the chocolate sponge start by separating 4 eggs
Into the egg whites, add the caster sugar and cream of tartar and mix with a food mixer or electric hand whisk to create stiff peaks
Into the egg yolks, add the other half of caster sugar and whisk together
Fold the egg white mixture into the egg yolk mixture in three lots
Melt the butter and add it to the egg mixture along with the plain flour and cocoa powder in two batches, folding in gently between each batch
Take the frozen 'pattern' tray out of the freezer and pour the mixture over it, give the tray a couple of bangs on the work surface to make sure there are no gaps.
Bake on 180C/160C Fan/350F/Gas Mark 5 for approx 7 - 8 minutes. When it is done, immediately flip it out onto some baking paper and peel off the paper on the top to reveal the pattern
Flipped it back over again onto some fresh baking paper and roll it up, taking the baking paper with it. Leave it to cool completely
To make the cream cheese filling mix together butter, cream cheese, lime juice and lime zest, and icing sugar
Unroll the sponge, spread the filling over it, then re-roll it
Serve immediately, store leftovers in the fridge and eat within 2 days