Preheat the oven to 180°C and grease and line 3 x 6 inch round cake tins with baking paper and cooking spray.
In a medium sized bowl, whisk together plain flour, cocoa powder, baking powder and bicarbonate of soda.
In a large mixing bowl, whisk together brown sugar, canola oil, and vanilla until combined. Add in the coffee and the white vinegar and mix to combine.
Slowly add the dry ingredients to the large bowl, alternating with the milk until batter just comes together.
Pour the batter evenly between the prepared cake pans and place in the oven to bake for 25-30 minutes, or until a toothpick when inserted in the centre comes out clean. The tops should also spring back when lightly touched. Let cool in the pans for about 20 minutes, before turning out to a wire rack to cool completely.
Once the cakes are cool, prepare a batch of vegan chocolate frosting and assemble the cake. If the cakes have domed in the oven, gently level the tops using a large serrated knife. Place a small amount of frosting on a cake plate/stand and place the first layer down. Cover with a layer of frosting before placing the second layer on top, upside down to ensure you have a flat top. Repeat with more frosting and the final cake layer. Cover the top and sides of the cake with another thick layer of frosting using a cake knife and gently smooth it around so the coverage is even. For this step I use a cake scraper but you can just use a knife - it doesn’t have to be perfect. Place the cake in the fridge to chill.
Make the ganache. Chop up the chocolate into small pieces (think the size of chocolate chips) and place it in a small bowl. Heat up the coconut milk in the microwave or on the stove until warm (not too hot!). Add the milk to the bowl with the chocolate pieces and let sit for a couple of minutes. The heat from the milk will melt the chocolate. Mix together using a spoon or whisk until glossy and all the chocolate has melted. If your chocolate isn’t melting, sit the bowl in another bowl of warm water. If the ganache is too thick, add more warm coconut milk a tablespoon at a time until you reach the desired consistency for your drip.
Decorate the cake. Put the warm chocolate ganache in a squeeze bottle while still warm and slowly use this to drip it down the sides of the chilled cake, starting from the top edge. Once you’ve gone around the edge, cover the top in a thin layer of the ganache. Set aside again in the fridge to set.
Once the ganache has hardened, put any remaining buttercream in a piping bag with your favourite tip attachment and pipe swirls around the top. Top with a little bit of grated dark chocolate if desired.