Make the vegan buttermilk. Mix together the soy milk and the vinegar. Set aside for 7-8 minutes so that it can curdle. Measure out the other ingredients in the meantime.
To a large mixing bowl, add the all-purpose flour, cocoa powder, brown sugar, baking powder, baking soda, salt. Mix to combine.
Next, pour in the buttermilk, the oil, vanilla extract and maple syrup. Carefully, fold your cake batter until there are no pockets of flour left.
Equally, pour the cake batter into the two prepared cake tins. Bake in the centre of the oven for 20 minutes. A skewer will come out completely clean when they are ready.
Let the cakes cool in their tins for 15 minutes, then remove the cakes from the tins. Transfer them to a cooling rack to so that they can cool down completely.