Preheat your oven to 350°F (175°C). Lightly grease a 9×13-inch baking pan or line it with parchment paper for easier removal. Set aside.

In a large mixing bowl, combine the yellow cake mix, water, vegetable oil, and eggs. Use an electric mixer on medium speed (or whisk by hand) to blend until the batter is smooth and no dry pockets remain. This should take about 2 minutes.

Pour the cake batter into the prepared baking pan. Use a rubber spatula to spread the batter evenly to the corners. Bake in the preheated oven for 22 to 25 minutes, or until a toothpick inserted in the center comes out clean. Be careful not to overbake.

Once baked, remove the cake from the oven and place the pan on a cooling rack. While the cake is still warm (but not hot), carefully spread the room temperature peanut butter over the top in an even layer. Let the heat from the cake slightly melt the peanut butter to make spreading easier.

Allow the cake with the peanut butter topping to cool completely at room temperature. This step is important so the frosting doesn’t melt when applied.

Once fully cooled, remove the lid and foil from the chocolate frosting tub. Microwave the frosting for 15–20 seconds, just enough to soften it for easier spreading (optional). Stir and then spread the chocolate frosting evenly over the peanut butter layer using a knife or offset spatula.

Chill the finished cake in the refrigerator for about 20–30 minutes or until the frosting sets. Once firm, slice into bars or squares and serve. Keep any leftovers stored in an airtight container at room temperature or refrigerated, depending on your preference.