1. Preheat your oven to 350°F (175°C) and prepare three 8-inch cake pans by greasing them with nonstick spray and lining the bottom with parchment paper.
2. In a large mixing bowl, whisk together 2 to 2.5 cups of all-purpose flour, 1.5 to 2 cups of granulated sugar, 2/3 to 3/4 cup of black cocoa powder, 1 to 1.5 tsp of baking soda, 2 tsp of baking powder, and 1/2 to 1 tsp of salt until well combined.
3. In a separate mixing bowl, combine 1/2 to 1.5 cups of vegetable oil, 1 cup of buttermilk, 2 to 3 large eggs, 2 tsp of vanilla extract, and 1 tbsp of vinegar. Mix until smooth.
4. Gradually mix the wet ingredients into the dry ingredients, stirring until just combined. Avoid overmixing to maintain a tender cake texture.
5. Add 1 cup of hot water or coffee to the batter, mixing gently until the batter is smooth, slightly runny, and free of lumps.
6. Divide the batter evenly among the prepared cake pans. Tap the pans on the counter to release any air bubbles.
7. Bake the cakes in the preheated oven for 30 to 40 minutes or until a toothpick inserted in the center comes out clean.
8. Allow the cakes to cool in the pans for 15 minutes, then transfer them to a wire rack to cool completely.
9. While the cakes cool, prepare the frosting by beating 1 to 2 cups of unsalted butter until smooth. Gradually add 1 to 1.5 cups of black cocoa powder, 5 to 6 cups of powdered sugar, and 2/3 to 4 tbsp of heavy cream or milk. Beat until creamy and fluffy. Add black gel food coloring if desired.
10. Once cooled, assemble the cake by placing one layer on a serving plate and spreading a generous amount of frosting over it. Repeat with the remaining layers.
11. Apply a crumb coat to the entire cake to seal in crumbs, then finish with a smooth, even layer of frosting for a polished look.
12. Chill the assembled cake in the refrigerator for about 30 minutes to set the frosting before serving or decorating further.
13. To serve, slice the cake into portions and enjoy its rich, moist flavor with family and friends.
14. Store leftover cake at room temperature in an airtight container for up to two days or refrigerate to prolong freshness. For long-term storage, freeze the cake appropriately.