Preheat the oven to 180C/350F degrees
Grease and line a rectangle baking tin ( 9 x 13 inch, 22.9cm x 33cm) with parchment paper.
In a medium bowl, whisk the egg whites until stiff peaks form.
In another medium bowl, beat the egg yolks, lemon juice,lemon zest, vanilla and allulose together.
Add the coconut flour, baking powder and salt. Mix well until smooth.
Gently fold in the egg whites until you have a light batter. Don’t overwork folding the egg whites in.
Pour the cake batter into the baking tin and smooth evenly.
Bake for 15-20 minutes until firm.
Remove the baking tin from the oven and allow to cool for 5 minutes.
Put a large piece of parchment paper on your countertop and place the baking tin on the parchment paper, sponge facing down. Remove the tin from the sponge.
Using the parchment paper on the top of the sponge, gently roll up the cake. This is to keep the sponge in the correct shape before adding the filling.
Set aside to cool.