Peanut Butter Texas Sheet Cake

Attention, peanut butter lovers! In this moist cake, the peanut butter is baked inside the cake and mixed with the icing... and sprinkle peanuts on top!
Combine flour, sugar, salt, and baking soda in a large bowl; set aside. Combine the butter, water, and peanut butter in a saucepan over medium-high heat; bring to a boil. Add to flour mixture and mix well; set aside. Combine the eggs, vanilla, and buttermilk; add to the peanut butter mixture.Place the dough in a greased 15-inch x 10-inch jelly roll pan. Bake at 350 degrees for 25-28 minutes, or until the pie begins to spring with a light touch. Spread the warm cake with peanut butter frosting and garnish, if desired.Peanut butter frosting: Combine the first 3 ingredients in a saucepan over medium-high heat; bring to a boil. Remove from heat; add the powdered sugar and vanilla, stirring until smooth.