Step 1: Preheat your oven to 350°F (175°C). Grease and flour two 8-inch round cake pans or line the bottoms with parchment paper.
Step 2: In a large bowl, whisk together the all-purpose flour, granulated sugar, black cocoa powder, baking soda, and salt.
Step 3: In a separate medium bowl, whisk together the buttermilk, vegetable oil, large eggs, white vinegar, and 1 teaspoon vanilla extract.
Step 4: Pour the wet ingredients into the dry ingredients and mix on low speed with an electric mixer until just combined. Be careful not to overmix.
Step 5: Slowly add the hot water or hot brewed coffee to the batter, mixing until smooth. The batter will be thin.
Step 6: Divide the batter evenly between the prepared cake pans.
Step 7: Bake for 30-35 minutes, or until a wooden skewer inserted into the center of the cakes comes out clean.
Step 8: Let the cakes cool in the pans for 10-15 minutes before inverting them onto a wire rack to cool completely. Ensure they are fully cooled before frosting.
Step 9: For the Cream Cheese Frosting: In a large bowl, beat the softened butter and softened cream cheese together with an electric mixer until smooth and creamy.
Step 10: Gradually add the sifted powdered sugar, one cup at a time, mixing until fully incorporated and smooth. Start with 4 cups and add more if you prefer a sweeter or stiffer frosting.
Step 11: Beat in 1 teaspoon vanilla extract and a pinch of salt. Continue to beat on medium-high speed for 2-3 minutes until the frosting is light and fluffy.
Step 12: Once the cake layers are completely cooled, frost the cake as desired, layering the frosting between the cake layers and covering the top and sides.