Chocolate Sheet Cake

Instructions

1. Prepare the baking pan
   Preheat oven to 350°F (175°C). Grease and flour a 10x15 inch jelly roll pan or a 9x13 inch baking pan.
2. Mix dry ingredients
   In a large bowl, whisk together flour, sugar, baking soda, and salt until well combined. Set aside.
3. Prepare chocolate mixture
   In a medium saucepan, combine 1 cup butter, 1/3 cup cocoa powder, and water. Bring to a boil over medium-high heat, stirring constantly. Remove from heat once it reaches a boil.
4. Combine ingredients
   Pour the hot chocolate mixture over the dry ingredients and stir until just combined. Add eggs one at a time, beating well after each addition. Stir in buttermilk and 1 teaspoon vanilla extract until smooth.
5. Bake the cake
   Pour batter into the prepared pan and spread evenly. Bake in preheated oven for 20-25 minutes, or until a toothpick inserted in center comes out clean or with a few moist crumbs.
6. Make the frosting
   About 5 minutes before the cake is done, prepare the frosting. In a medium saucepan, combine 1/2 cup butter, 1/4 cup cocoa powder, and milk. Bring to a boil, stirring constantly. Remove from heat and gradually stir in powdered sugar and 1 teaspoon vanilla extract until smooth and glossy.
7. Frost the cake
   Pour the warm frosting over the hot cake as soon as it comes out of the oven, spreading it evenly across the surface. The heat from both the cake and frosting will help it spread easily.
8. Cool and serve
   Allow the cake to cool completely at room temperature before cutting into squares. For the best texture and flavor, let it rest for at least 1 hour before serving.