Instructions
1. Preheat the Oven:

Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans, or line them with parchment paper for easy removal.
2. Mix the Dry Ingredients:

In a large bowl, whisk together the flour, sugar, cocoa powder, baking powder, baking soda, and salt. Make sure the dry ingredients are well combined and free of any lumps.
3. Add the Wet Ingredients:

Add the eggs, buttermilk, vegetable oil, and vanilla extract to the dry ingredients. Use a hand mixer or stand mixer to beat the mixture on medium speed for about 2 minutes, until everything is smooth and well incorporated.
Add the sour cream (if using) and continue to mix until combined.

4. Add the Hot Water (or Coffee):

Gradually add the hot water (or hot coffee) to the batter. The batter will be very thin, which is normal. This step helps keep the cake ultra-moist.