1-Getting started with this Chocolate Sheet Cake With Peanut Butter Frosting is straightforward, and it begins with preheating your oven. Set it to 350°F (177°C) and grease a 12×17-inch half sheet pan to avoid any sticking issues. This step ensures your cake comes out clean and ready for frosting.

2-In a saucepan, heat the unsalted butter, water, and unsweetened natural cocoa powder over medium heat, whisking until everything melts and becomes smooth. In a large bowl, whisk together the all-purpose flour, baking soda, and salt to create a solid base. Pour the warm chocolate mixture into the dry ingredients and whisk until combined and thick, which helps build that moist texture everyone loves.

3-Next, in another bowl, whisk the eggs, granulated sugar, packed light brown sugar, and pure vanilla extract until they’re well mixed, then blend this into the chocolate batter. Stir in the buttermilk to add extra moisture. Pour the batter into your prepared pan, tap it gently to remove air bubbles, and bake for 15-20 minutes or until a toothpick inserted in the center comes out clean. Let the cake cool completely before moving on to the frosting.

4-For the peanut butter frosting, beat the creamy peanut butter and unsalted butter on medium-high speed for about 2 minutes until smooth. Add the confectioners’ sugar, heavy cream (or half-and-half or whole milk), pure vanilla extract, and a pinch of salt. Start on low speed for 20 seconds, then increase to high until the mixture is fluffy. Adjust as needed by adding more sugar to thicken or more cream to thin, then spread it over the cooled cake and top with optional melted peanut butter or chopped peanut butter cups. The total preparation time is about 30 minutes prep, 20 minutes cook, and around 2 hours and 50 minutes including cooling and frosting.