Preheat the oven to 325 degrees F. Spray three 8-inch or four 6-inch round cake pans with nonstick spray. Line the bottom of each pan with parchment paper and spray the pans again.
Combine the flour, sugar, cocoa, baking soda, baking powder, and salt into the bowl of an electric mixer fitted with a paddle attachment and mix on low speed until combined. Add the zest and mix until combined.
In another bowl, combine the buttermilk, oil, eggs, coffee or water and vanilla.
With the mixer on low speed, slowly add the wet ingredients to the dry, scraping the bottom of the bowl with a rubber spatula.
Pour the batter evenly into the prepared pans and bake for about 23 t0 28 minutes.
Cool in the pans for 10 minutes, then turn them out onto a cooling rack and cool completely.
Wrap in plastic wrap and chill until ready to use. You're still going to want to level your cake layers to ensure a completely even surface for frosting and stacking.