You need to work quickly making this so have a prepared large flat baking tray ready to set the popcorn and all the ingredients to hand.
Add the sugar and water to a large pot on a medium-low heat. Don't stir but you can shake to stop it burning.
Once the sugar turns a deep caramel colour, remove from the heat and add the tablespoon of dairy-free butter. It will bubble up, keep stirring until smooth.
Then pour over the bowl of popped corn. Quickly transfer to the tray to set.
To make the chocolate cake
Preheat the oven to 180C / 350F and grease and line two 8-inch cake tins.
Mix all the dry ingredients into a large bowl, then whisk in the wet ingredients, leaving the apple cider vinegar til the last minute, as it will react with the rising agents to help make the cake fluffy and risen.
Pour the batter equally between the two cake tins and bake for approximately 35 minutes or until a toothpick poked into the middle of the cake comes out clean.
Once baked, leave to cool completely before removing from the tins. Then freeze the two layers for a few hours, so it's easier to trim.
Remove from the freezer and trim the tops to make them even. Now slice each layer in half, length-ways, to create four cake layers.