Preheat your oven to 350°F (177°C) and rub two 9 inch round cake pans with oil and then dust them with flour to prepare them for the batter.
Make the chocolate cake batter
Measure the dry ingredients (flour, sugar, cocoa powder, baking soda, and salt, into a large mixing bowl) and give them a stir with a whisk.
Measure the wet ingredients (water, oil, vinegar, and vanilla) in a separate bowl (I measure them all in a large measuring container).
Pour the wet ingredients into the dry ingredients.
Stir with a whisk until you have a smooth batter and you can no longer see dry flour.
Bake your cake
Immediately pour the batter into your prepared cake pans and bake at 350°F (177°C) for 35-40 minutes or until a toothpick inserted in the middle comes out clean.
Allow it to cool for 30 minutes in the cake pan then invert them onto a plate in the refrigerator to cool completely before frosting.
Assemble the cake
Put your first cake top side down on your serving dish.
Top with a thick layer of buttercream, jam, or jelly to stick the two layers together.
Put your next layer on the top right side up.
Frost the cake with a thick layer of chocolate vegan buttercream or any other flavor you would like.
Notes
Spoon your flour into the measuring cup and level it off with the back of a butter knife. Don’t scoop out the flour out of the bag with a measuring cup. This will pack the flour down too much resulting in too much flour.
Don't over stir the batter or the cake will have a chewy texture.
Don't let the batter sit once you have added the wet ingredients or the baking soda and vinegar will stop interacting by the time you bake the cake.
If you take the cake out of the oven and it deflates in the center, it is not done. Quickly put it back in the oven for at least 5 more minutes.
Let the cake cool for at least 30 minutes before inverting the pans and taking the cake out.
Allow the cake to cool completely before frosting. Colder cakes are easier to frost and will not have as many crumbs when you frost it.