Step 1: Preheat oven to 350 degrees Fahrenheit. Grease a 9x13 inch baking dish with cooking spray or butter.
Step 2: In a large mixing bowl, whisk together the flour, sugar, cocoa powder, baking powder, baking soda, and salt until well combined.
Step 3: Add in the buttermilk, vegetable oil, eggs, and vanilla extract. Mix until the batter is smooth and free of lumps.
Step 4: Slowly pour in the hot water while stirring continuously to prevent the batter from curdling.
Step 5: Pour the batter into the prepared baking dish and smooth out the top with a spatula.
Step 6: Bake for 30-35 minutes or until a toothpick inserted in the center comes out clean.
Step 7: Let the cake cool completely before frosting. Use your favorite chocolate frosting recipe or store-bought frosting to decorate the cake. Enjoy!