Step 1: Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans, or line them with parchment paper.
Step 2: In a large bowl, whisk together the granulated sugar, all-purpose flour, unsweetened cocoa powder, baking soda, baking powder, and salt. Ensure all dry ingredients are well combined and lump-free.
Step 3: In a separate medium bowl, whisk together the buttermilk, vegetable oil, eggs, and vanilla extract until smooth.
Step 4: Pour the wet ingredients into the dry ingredients. Mix on low speed with an electric mixer, or by hand, until just combined. Be careful not to overmix the batter.
Step 5: Carefully pour in the hot coffee (or hot water). Stir until just combined. The batter will be quite thin, which is normal for this recipe.
Step 6: Divide the batter evenly between the two prepared cake pans. For best results, use a kitchen scale to ensure even layers.
Step 7: Bake for 30-35 minutes, or until a wooden skewer or toothpick inserted into the center of the cakes comes out clean. Baking time may vary by oven.
Step 8: Remove the cakes from the oven and let them cool in their pans on a wire rack for 10-15 minutes.
Step 9: After initial cooling, carefully invert the cakes onto the wire rack to cool completely before frosting. Ensure they are fully cooled to prevent frosting from melting.
Step 10: Once completely cool, frost with your favorite chocolate buttercream, ganache, or cream cheese frosting. Decorate as desired.