Preheat your oven to 350°F and grease a 10×15-inch sheet cake pan. Texas sheet cakes are traditionally baked in a large shallow pan, which helps create a thin, moist cake with lots of frosting in every bite.

In a large mixing bowl, whisk together the flour, sugar, salt, and baking soda until combined.

In a saucepan over medium heat, combine the butter, vegetable oil, cocoa powder, and water. Stir continuously until the butter melts and the mixture becomes smooth and hot, but not boiling.

Pour the warm chocolate mixture into the dry ingredients and stir gently until combined.

Add the buttermilk, eggs, and vanilla extract. Mix until the batter becomes smooth and glossy. Do not overmix because that can make the cake less tender.

Pour the batter into the prepared sheet pan and spread evenly.

Bake for 18 to 22 minutes or until a toothpick inserted into the center comes out with a few moist crumbs attached.

Allow the cake to cool completely before adding the peanut butter layer.

For the peanut butter filling, beat together the peanut butter, powdered sugar, cream cheese, and heavy cream until smooth and fluffy. Spread evenly over the cooled cake.

To prepare the frosting, melt the butter in a saucepan and whisk in the cocoa powder and milk until smooth. Remove from heat and gradually whisk in the powdered sugar and vanilla until creamy.

Let the frosting cool slightly, then spread it carefully over the peanut butter layer. Sprinkle with chocolate chips and chopped peanuts while the frosting is still soft.

Refrigerate the cake for at least 1 hour before slicing so the layers can fully set.