Chocolate Sheet Cake with Peanut Butter Frosting

Fudgy beyond rich chocolate sheet cake topped with the creamiest peanut butter frosting. Feeds a crowd! I encourage you to read the full recipe and the recipe notes before beginning so youre completely prepared.
Ingredients
1 cup 16 Tbsp 226g unsalted butter
1 cup 240ml water
12 cup 41g unsweetened natural cocoa powder not dutchprocess
2 cups 250g allpurpose flour spooned leveled
1 teaspoon baking soda
14 teaspoon salt
2 large eggs at room temperature

1 cup 200g granulated sugar
12 cup 100g packed light brown sugar
2 teaspoons pure vanilla extract
12 cup 120ml buttermilk at room temperature
Peanut Butter Frosting
1 and 12 cups 405g creamy peanut butter do not use natural style
12 cup 8 Tbsp 113g unsalted butter softened to room temperature
3 cups 360g confectioners sugar
12 cup 120ml heavy cream halfandhalf or whole milk
1 teaspoon pure vanilla extract
pinch salt
optional 12 cup 135g melted creamy peanut butter and 1 cup chopped peanut butter cups
Instructions
Preheat oven to 350F 177C. Generously grease a 1217inch half sheetjelly roll pan. Set aside.
Heat the butter water and cocoa powder together in a large saucepan over medium heat. Whisk constantly until the butter has melted and everything is smooth and combined. Set aside. In a large bowl whisk the flour baking soda and salt together. Pour the warm chocolatebutter mixture on top then slowly whisk together until combined. It will be very thick.
Whisk the eggs granulated sugar and brown sugar together in a medium bowl. The mixture will be thick. Whisk in the vanilla until combined then pour into the chocolate batter and whisk until combined. Finally whisk in the buttermilk. Pour the chocolate batter into the sheet pan.
Bake for 1520 minutes. Mine takes exactly 17 minutes. Use a toothpick to test for doneness stick it into the cake. If the toothpick comes out clean the cake is done. If not continue baking. Remove cake from the oven and set the pan