Preheat your oven to 350°F (175°C). Grease and flour a 9x13-inch baking pan.
In a large mixing bowl, combine the flour, sugar, cocoa powder, baking powder, baking soda, and salt. Whisk together until well blended.
Add the vegetable oil, buttermilk, eggs, and vanilla extract to the dry ingredients. Mix on medium speed for about 2 minutes until smooth.
Carefully stir in the boiling water until fully combined. The batter will be thin.
If desired, fold in the chopped nuts and chocolate chips.
Pour the batter into the prepared baking pan and bake for 30-35 minutes, or until a toothpick inserted in the center comes out clean.
Allow the cake to cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely.