- Preheat oven to 350F (175C). Grease and flour a 9-inch round cake pan. 
- In a large bowl, whisk together flour, cocoa powder, baking soda, baking powder, and salt. 
- In a separate bowl, combine sugar, buttermilk, vegetable oil, egg substitute, and vanilla extract. Mix well. 
- Gradually add the wet ingredients to the dry ingredients, mixing until just combined. Do not overmix. 
- Slowly pour in the boiling water and stir until the batter is smooth and thin. 
- Pour the batter into the prepared cake pan. 
- Bake for 30-35 minutes, or until a wooden skewer inserted into the center comes out with moist crumbs attached. 
- Let the cake cool in the pan for 10 minutes before inverting it onto a wire rack to cool completely. 
- Frost with your favorite chocolate frosting. 
- For a richer chocolate flavor, add cup of chocolate chips to the batter. Adjust baking time if using a different size or shape of pan. To prevent sticking, line the bottom of the cake pan with parchment paper.