First up reduce your aquafaba, this makes it easier to whip up. Pop 200ml of aquafaba in a saucepan over a medium heat, leave to simmer until it has halved in volume, you should be left with 100ml. pop in the fridge to cool and thicken, and once cool it will have a similar consistency to egg white. 

Once your aquafaba has cooled. Preheat the oven to 180°C/160°C fan/Gas Mark 4 and grease and line a shallow baking tray approx. 32cmx23cm. 

Pop the aquafaba in a large grease-free bowl with the Cream of Tartar. Whisk together on a high speed for about 8-10 minutes until stiff peaks form. 

In a separate bowl mix together the dry ingredients and then add the melted vegan butter, soy milk and Vanilla Extract and combined and smooth, the mixture will be very thick. Once your aqaufaba is whipped up, add half to your mixture and gently fold through to combine. Add the rest of the aquafaba and fold through until you have a lovely smooth mixture. 

Pour the mixture into your prepared baking tray and smooth to evenly cover. Bake for 12-15 minutes until the sponge springs back when pressed. Leave your sponge in the tin and cover with a clean tea towel to cool, we know you’ll be tempted to roll up your sponge whilst it’s warm but trust use it’s easier once it has cooled.

Whilst your sponge is cooling, it’s time to make the buttercream;  
melt the Dark Chocolate in a heat proof bowl by placing in a microwave on high heat in 30 second blasts, stirring in between blasts until melted. Put to one side to cool slightly.

In a freestanding mixer/or large bowl with electric hand mixer beat the butter until pale in colour. Add the Orange Extract and sift in the icing sugar and beat again until light and fluffy. Add in the cooled, melted chocolate and mix again until well combined.

Once your sponge is cooled, spread evenly with half of the chocolate orange buttercream. Carefully roll up the sponge starting at the shorter edge. It is easier to roll the sponge up in the tin and use the greaseproof paper on the base of the sponge to help you roll it. Don’t worry if your sponge cracks as you roll it, it is very delicate - you can cover the crack up with more buttercream when you decorate it. 

Carefully transfer the sponge onto a serving plate with the seam at the base. Cover the roll with the remaining buttercream, creating ridges to look like the texture of bark, using a fork or palette knife.

Put the roll in the fridge to firm up for about an hour. Dust with Cocoa Powder and sprinkling or orange zest to serve. Serve at room temperature.