Peanut Butter Sheet Cake

Bryce first made this for my birthday when I was nursing Abigail and couldn't eat chocolate!

Cake:
2 cups all-purpose flour
2 cups white sugar
1/2 teaspoon baking soda
1/4 teaspoon salt
1 cup water
3/4 cup butter, softened
1/2 cup peanut butter
1/4 cup oil
2 eggs
1/2 cup buttermilk
1 teaspoon vanilla extract

Frosting:
2/3 cup white sugar
1/3 cup evaporated milk
1 tablespoon butter
1/3 cup peanut butter
1/3 cup mini marshmallows
1/2 teaspoon vanilla extract

Directions:
1. Preheat oven to 350 degrees F (175 degrees C). Grease a 10x15x1 inch jelly roll pan. (or line with parchment paper).
2. In a large bowl, stir together the flour, 2 cups sugar, baking soda and salt.  Set aside. Combine the water and 3/4 cup butter in a saucepan and bring to a boil.  Remove from the heat and stir in 1/2 cup peanut butter and oil until well blended.  Stir this mixture into the dry ingredients.  Combine the eggs, buttermilk, and vanilla; stir into the peanut butter mixture until well blended.  Spread the batter evenly in the prepared pan.
3. Bake for 18 to 26 minutes in preheated oven, or until a toothpick inserted near the center comes out clean.
4. While the cake bakes, place 2/3 cup sugar, evaporated milk, and butter into a saucepan. Bring to a boil, stirring constantly.  Cook stirring or 2 minutes.  Removed from heat and stir in the peanut butter marshmallows and vanilla until marshmallows are melted and the mixture is smooth.
5. Spoon the frosting over the warm cake and spread in an even layer.  Allow to cool before cutting and serving.

Recipe from Allrecipes.com