Step 1: Prepare the Cake Batter Start by preheating your oven to 350°F (175°C). In a large mixing bowl, combine the flour, sugar, and salt, giving them a quick whisk to distribute the ingredients evenly. In a saucepan over medium heat, melt the butter. Once melted, add the cocoa powder, stirring vigorously until they form a smooth mixture. Add the boiling water and allow the mixture to boil for 30 seconds, then turn off the heat. Carefully pour this hot cocoa mixture over the flour mixture in your mixing bowl, stirring lightly to combine. This step might seem unusual, but it actually helps to “bloom” the cocoa, releasing maximum chocolate flavor while slightly cooking the flour. In a separate measuring cup, pour the buttermilk and add the beaten eggs, baking soda, and vanilla extract. Whisk these ingredients together until well combined, then gradually stir this mixture into the butter and chocolate mixture.

Step 2: Baking the Cake Pour the batter into an 18-by-13-inch sheet cake pan. One of the great things about this recipe is that you typically don’t need to grease the pan the butter content in the batter prevents sticking! Place the pan in your preheated oven and bake for 20 minutes, or until a toothpick inserted into the center comes out clean. Avoid overbaking, as this can lead to a dry cake. The high butter content means this cake bakes relatively quickly compared to other cake recipes.

Step 3: Making the Icing While the cake is baking, it’s time to prepare the signature icing that makes this chocolate sheet cake so special. The timing here is perfect since you’ll apply the icing while the cake is still warm. In a saucepan, melt the butter (1/2 cup plus 6 tablespoons). Once melted, add the cocoa powder, stirring to combine completely. Remove the pan from the heat and gradually add the milk and vanilla extract, stirring continuously. Slowly add the powdered sugar (1 pound minus 1/2 cup), stirring until smooth. The mixture will thicken beautifully. Finally, fold in the finely chopped pecans, distributing them evenly throughout the icing.

Step 4: Finishing Your Masterpiece Once the cake comes out of the oven, immediately pour the warm icing over the warm cake. This technique allows the icing to seep slightly into the cake, creating an incredibly moist and flavorful result. Use a spatula or knife to spread the icing evenly over the entire surface. Work quickly, as the icing will begin to set as everything cools. Cut into squares and serve! This chocolate sheet cake is fantastic slightly warm, at room temperature, or even chilled the next day.