Yield: 24 servings.
For the cake:
2 cups all-purpose flour
2 cups sugar
1 teaspoon salt
1 teaspoon baking soda
½ cup crunchy peanut butter (do not use natural)
1 cup water
1 stick unsalted butter
½ cup canola oil
1 teaspoon vanilla extract
2 large eggs, at room temperature, slightly beaten
½ cup buttermilk, at room temperature
For the frosting:
1 stick salted butter, softened
½ cup creamy peanut butter
6 tablespoons buttermilk
1 teaspoon vanilla
3 cups powdered sugar, sifted
Preheat oven to 350°. Prepare a 9 x 13-inch pan with cooking spray and set aside. In a large bowl, whisk together flour, sugar, baking soda, and salt. Set aside.
In a saucepan, add water and butter; heat on medium and bring to a slow boil. Remove from heat; stir in peanut butter and oil until well blended. Mix in eggs, buttermilk, and vanilla until blended.
Pour batter into flour mixture. Mix until all ingredients are incorporated. Batter will be loose. Pour into the prepared pan, spreading evenly to all corners. Bake at 350° for 45 minutes, or until a toothpick inserted in the center comes out clean. Remove from oven.
To make the frosting, bring butter, peanut butter, and buttermilk to a rapid boil. Remove from heat and gradually whisk in vanilla and powdered sugar. While the frosting is still hot, spread over the warm cake. Let cake cool completely and cut into bars.