Begin by preheating you oven to 180C / 356F / gas mark 4 and lining a 33 x 23cm Swiss roll tin with grease proof paper.
Before you begin baking, whisk together the apple cider vinegar and plant milk and let it rest for 5-10 minutes until it curdles to form vegan buttermilk.
Next add the flour, sugar, cocoa powder and baking sugar to a large mixing bowl and whisk to combine.
Melt the non-dairy butter and add to the dry ingredients along with the vegan buttermilk.
Whisk the wet and dry ingredients until they are well incorporated and the cake batter is smooth.
Pour the cake batter into the tin and smooth out with a palette knife.
Place the tin into the centre of the oven and bake for 15 - 20 minutes or until it is smooth on the surface.
Remove from the oven and leave it to cool for 5 minutes before attempting to turn it out.
While the cake cools, lay out a clean tea towel then cover this with a large piece of grease proof paper. Sprinkle the grease proof paper with a little caster sugar.
Turn the sponge out on to the sugared grease proof paper then peel off the grease proof paper that was used to originally line the tin.
Take the grease proof paper which the cake is sitting on and tightly curl it, and the sponge cake to form a tight swirl. Wrap it in the tea towel and leave to cool completely.