Chocolate Sheet Cake

Instructions

1. Preheat the oven to 350 degrees F.
2. In a large bowl, whisk together the flour, sugar and salt. In a separate bowl, whisk together the buttermilk, eggs, vanilla and baking soda.
3. In a medium saucepan, melt the butter and add the cocoa; whisk to combine. Add the boiling water to the pan, mix and heat until bubbling, then turn off the heat. Pour the hot chocolate mixture into the flour mixture and stir to combine. Pour in the egg mixture and stir together until smooth. Pour into an ungreased, nonstick 12x18-inch rimmed pan (jelly roll pan), and bake for about 20 minutes, or until the cake is set and no longer gooey in the middle.
4. While the cake is baking, make the icing. Melt the butter in a medium-large saucepan over medium heat. Add the cocoa powder and stir until smooth. Pull the pan off the heat. Add the milk and vanilla, then stir in the powdered sugar. Use a whisk and stir vigorously to get all of the lumps out. Pour the warm icing over the cake as soon as it comes out of the oven. Try and pour it over the cake evenly and spread it out quickly to cover the top, then don't mess with it. If you want sprinkles or nuts on top, sprinkle those on immediately. Let the cake sit at room temperature until ready to serve.