Preheat the oven to 350°F (180°C) and spray two 8-inch cake pans (*see notes) with non-stick spray and line the bottoms with circles of parchment paper. Set aside.
Sift all purpose flour and cocoa powder into a mixing bowl and add white granulated sugar, baking soda, baking powder, salt and instant espresso powder. Mix together.
Prepare your vegan buttermilk. Add apple cider vinegar to a measuring jug and then add soy milk up to the 1 cup (240ml) line. Let it curdle into vegan buttermilk.
Prepare the flax eggs. Add 2 tablespoons of ground flaxseed to a bowl and add 6 tablespoons of hot water. Let it sit for a minute to thicken and become gloopy.
Add the vegan buttermilk to the mixing bowl along with the flax eggs, oil and vanilla extract. Stir into a thick batter. Don't over-mix.
Add hot water and whisk it in with a hand whisk. The batter will be thin but this is exactly how it is supposed to be.
Divide the batter evenly between the two prepared 8-inch cake pans.
Bake for 35 minutes or until a toothpick inserted into the center of one of the cakes comes out clean.
Let the cakes cool in the cake pans for a few minutes before removing from the cake pans and transferring to a wire cooling rack to cool completely before frosting.
Frost with vegan chocolate buttercream frosting.