Preheat oven to 350˚F (175˚C) and grease two 8-inch (20cm) cake pans. (You can also line them with parchment paper for easier removal).
In a measuring jar, add non-dairy milk and vinegar. Stir to combine and set aside until it curdles to create vegan buttermilk.
Sift the flour, cornstarch, sugar, cocoa powder, baking powder, baking soda, and salt into a large bowl and give a good whisk to combine.
Add the melted coconut oil, applesauce, vanilla, and vegan buttermilk. Mix on medium speed using a handheld mixer until well combined. Lower the speed and pour in the coffee, continuing to mix until combined. (If you like the cake sweeter, add more sugar to taste).
Divide the batter evenly into the prepared cake pans. Bake for 30 minutes, or until a toothpick inserted in the center comes out clean. (Please do not overbake, if you want a moist chocolate cake).
After baking let the cakes cool for 10 minutes in the pan, then remove and let them cool completely before frosting.