Pre-heat oven to 350 degrees F. Grease two 6 inch cake pans(you can also line the base with a circle of parchment paper if you’re worried it won’t come out).
In a medium bowl, stir together the milk and vinegar. Set aside for 3 minutes. This combo makes the vegan buttermilk.
Add the sugar, oil, and vanilla to the bowl with the milk. Whisk to combine.
In a large bowl, whisk together the flour, cocoa powder, baking soda, and salt until combined.
Pour the wet to the dry mixture and whisk until smooth. Careful not to overmix.
Divide the batter evenly between the two cake pans and smooth out the tops. Bake for 25-30 minutes. The cake is done when it slowly springs back when touched and a toothpick comes out clean. Place pans on the cooling rack for 15-20 minutes. Now slide a butter knife around the cake to loosen the edge. Gently and carefully invert the cakes onto a cooling rack. Let it cool completely.
While cakes are baking, make the coconut pecan filling. In a glass measuring cup or bowl, add the coconut milk and cornstarch. Whisk until well combined. In a medium saucepan over medium heat, melt the vegan butter. Add the sugars and coconut milk mixture. Stir with a spatula for about 5 minutes until mixture is bubbling and starts to thicken. Remove from heat and add the vanilla, coconut, and pecans. Stir until well combined. Transfer to a bowl and let it cool completely before using.
Once cakes and filling are cooled, you can start to assemble. Place one layer of cake on a plate or cake stand. Spread half of the coconut pecan filling on top and then add the second layer of cake. Top with the rest of the filling. Slice and enjoy!