Preheat the oven to 180C/350F degrees.
Grease and line a long rectangle baking tin with parchment paper. My tin is about 8 inches by 12 inches.
Whisk the egg whites until stiff.
In another bowl whisk the egg yolks and erythritol together.
Add the remaining cake ingredients to the egg yolk mixture and combine well.
Fold in the egg whites to the cake mixture.
Spoon into the baking tin and smooth evenly.
Bake for 20 minutes until firm.
Remove from the oven and place a piece of parchment paper over the cake whilst still warm (be careful not to burn yourself!).
Remove the cake from the tin, keeping the parchment paper on the bottom of the tin so that the cake has parchment paper either side of it.
Gently roll the cake from the smaller edge into a swiss roll shape. This will make it easier to unroll and fill later.
Set aside to cool.
Once the cake is cool, gently unroll the cake from the parchment paper and spread with the cranberry chia jam. Add an even layer of the whipped cream.
Gently roll the cake back into the swiss roll shape.
Place in the fridge for at least 30 minutes to help keep its shape.
Make the topping by blending the butter and cream cheese together until smooth.
Add the erythritol and cocoa powder and beat until smooth and blended.
Smoother the topping all over the cake.
Keep in the fridge to firm up the topping.
Eat and enjoy!