Ingredients
Method
Instructions
- Preheat oven to 350°F (175°C). Grease a 15x10x1-inch jelly roll pan with butter or cooking spray. Line with parchment paper if desired.
- In a large mixing bowl, whisk together the flour, sugar, baking soda, and salt until well combined. Set aside.
- In a medium saucepan, combine the butter, water, and cocoa powder. Bring to a boil over medium heat, stirring constantly. Once boiling, remove from heat immediately.
- Pour the hot chocolate mixture over the dry ingredients and stir until just combined. Add the buttermilk, eggs, and vanilla extract. Mix until smooth and no flour streaks remain.
- Pour the batter into the prepared pan and spread evenly. Bake for 20-25 minutes, or until a toothpick inserted in the center comes out clean.
- While the cake is baking, make the icing. In a saucepan, combine butter, cocoa powder, and milk. Bring to a boil, then remove from heat. Stir in vanilla extract, then gradually whisk in the powdered sugar until smooth. Stir in nuts if using.
- As soon as the cake comes out of the oven, pour the warm icing over the hot cake. Use a spatula to spread it evenly.
- Allow the cake to cool completely in the pan before cutting into squares. This typically takes about 1-2 hours at room temperature.
Notes
For best texture, spoon flour into measuring cup and level off with a knife. Buttermilk substitute: add 1½ teaspoons white vinegar or lemon juice to ½ cup milk and let sit 5 minutes. The icing should be pourable but not too thin - if it thickens too much, gently reheat with a splash of milk.