Prepare three 8 inch cake pans. Grease the inside of each pan by evenly coating them with butter. Use a paper towel to wipe up any excess butter. Sift ¼ cup cocoa powder into a separate bowl. Sprinkle the sifted cocoa powder on the buttered surface, turning the pan upside down over parchment paper to tap out any excess. This process helps the cake release from the pan more easily.
If you are using buttermilk, skip this step. If not, mix your preferred milk (regular, oat or almond works) with ¾ teaspoon of cream of tartar. Whisk to combine and let set.
In a medium-bowl, combine the all-purpose flour, sugar, cocoa powder, baking powder, baking soda and salt. Whisk to combine.
In a separate large bowl, combine the sour cream, eggs, buttermilk (or buttermilk substitute prepared in Step 2), vegetable oil, vanilla extract and coffee/espresso. Make sure the coffee/espresso is cool to the touch before combining it with the rest of the dry ingredients.
Add the dry ingredients to the bowl with the wet ingredients. Using a hand mixer, combine the ingredients well for about one minute. Be mindful not to overmix.
Distribute the batter evenly between the three pans. Bake for 35-40 minutes at 350° F. Test doneness by inserting a toothpick in the center of the cake. If it comes out clean, the cake is done.
Rest the cakes for 10 minutes. Then turn the cakes out onto a wire rack to cook completely.