Preheat the oven to 350°C. Line an 8" cake pan with parchment & oil.
In a small bowl, mix the flax seed and water together. Stir and allow to sit for 5 minutes.
In a small glass, pour the non-dairy milk and vinegar together. Allow to sit for 5 minutes.
In a bowl, mix the dry ingredients (flour, sugar, baking soda, baking powder, salt, cocoa powder). Mix with a whisk to remove the cocoa powder lumps. Set aside.
In another bowl, mix the wet ingredients (flax seed mixture, oil, non-dairy milk mixture, coffee and vanilla extract).
Pour the wet ingredients into the dry ingredients. Mix well. Pour into the cake pan, and bake at 350°C for 20-25 minutes or until a toothpick inserted comes out clean. It doesn't matter if the cake is slightly underdone, since it's edible even when raw.
Cool for 15 minutes.
Place the cooled cake onto your serving platter.