Preheat the oven to 350F & then grease & parchment line 4-6"cake pans
Combine the vegetable oil with the melted vegan butter & add the vanilla extract ~set aside
Combine the plant milk with the vinegar & let stand for 5 minutes to thicken. (Soy milk is the only plant milk that will thicken, but you can use another milk if you prefer)
Sift all the dry ingredients together in a large mixing bowl, including the sugar.
Pour in the wet ingredients (this will be the plant milk mixture & the butter/oil mixture) & whisk smooth about 30 strokes
Divide the batter into 4 separate bowls (it is helpful to weigh each portion so that each layer is the same size but it is not necessary just do your best to eye the amounts equally)
Now combine the cocoa powder with the oil in a medium bowl & whisk to a smooth paste
One portion of batter stays vanilla so be sure to move that aside. To one bowl of batter add 4 tablespoons of the cocoa paste & mix smooth this is the most intense chocolate layer
To another bowl of batter add 3 tablespoons of the cocoa paste & the remaining cocoa paste to the last bowl. Compare all the bowls of batter to make sure you have 4 different shades, if not you can always add a scoop from one into another to get the right shade you are looking for.
Scrape the separate batter shades into the prepared cake pans & bake in the preheated oven for approximately 18-22 minutes
While the cake layers are baking prepare the ganache & mocha buttercream recipes according to the instructions on those posts.
Once the cake layers are baked & cooled to cold & your icing recipes are ready assemble the cake as shown in the picture with the chocolate layer on the bottom filling each layer with a portion of the mocha buttercream
Crumb coat the cake with the buttercream but be sure to reserve about ½ cup of the buttercream for the rosettes decor on top.
Refrigerate the entire cake to cold then pour the warm *not hot ganache over the entire cake on a glazing rack set over a sheet pan with parchment paper to catch the excess drips
Garnish with optional cacao nibs & mocha buttercream rosettes