- Preheat oven to 350F (175C). Grease and flour a 9x13 inch baking pan. 
- In a large bowl, whisk together flour, sugar, cocoa powder, baking powder, baking soda, and salt. 
- Add buttermilk, oil, eggs, and vanilla extract to the dry ingredients. Beat with an electric mixer on medium speed for 2 minutes. 
- Gradually add the boiling water to the batter, mixing until combined. The batter will be thin. 
- Pour the batter into the prepared pan and bake for 30-35 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs. 
- Let the cake cool completely in the pan before frosting. 
- To Prepare the Frosting: 
- In a large bowl, beat the softened butter with an electric mixer until creamy. 
- Gradually add the powdered sugar and cocoa powder, alternating with the milk, beating until smooth and creamy. 
- Stir in the vanilla extract. 
- Frost the cooled cake evenly. 
- Slice, serve, and enjoy! 
- Tips & Substitutions: 
- For a richer flavor, substitute coffee for the boiling water. 
- To make the cake gluten-free, use a 1:1 gluten-free all-purpose flour blend. 
- *For a vegan version, substitute the buttermilk with a mixture of plant-based milk and lemon juice, use flax eggs instead of chicken eggs, and ensure the frosting ingredients are also plant-based.