Preheat oven to 350 degrees F / 175 degrees C. Grease four 6-inch or three 7-inch cake pans with homemade cake release or non-stick baking spray and parchment paper. Set aside. In a medium bowl, sift together the cake flour, cocoa powder, baking soda, and salt.
In a large bowl or the bowl of a stand mixer, use either a hand mixer or a stand mixer to cream together the butter and granulated sugar. Mix on a medium-high speed for 1-2 minutes, until the mixture becomes lighter in color. Scrape the sides and bottom of the bowl as needed with a rubber spatula.
Mix in the eggs on a medium speed until fully incorporated.
Add in the buttermilk, oil, green gel food coloring, vanilla extract, and white vinegar. Mix on a low speed until combined. The mixture might look broken at this stage, but I promise it will come together once we add in the dry ingredients.
Slowly mix the dry ingredients into the wet ingredients on low speed in two installments. Mix until just combined and you can no longer see any visible streaks of cake flour.
Divide the batter evenly between the prepared pans and bang the pans on your counter a few times to release any air bubbles that might be trapped in the batter. Bake for 28-32 minutes, or until a toothpick inserted in the center of the cake comes out with a few moist crumbs.
Remove the pans from the oven and let them cool for 10 minutes, then run a small offset spatula around the perimeter. Carefully flip the layers out of their pans and place on a wire rack to finish cooling. Level the cake layers with a serrated knife once they're fully cooled. If you're making these in advance, wrap and freeze them at this point.