Mix in large mixing bowl:  2 cups flour, 2 cups sugar and 1 tsp soda.

Boil:

2 sticks margarine

4 tablespoons cocoa powder

1 cup water

1 teaspoon vanilla

1/2 cup buttermilk

Pour boiled mixture over dry ingredients and mix with electric mixer. Pour into greased and floured 13 x 9 baking pan.

Bake for 25 minutes at 350. 

Let cool some and drop peanut butter in globs over top of cake.  Spread like you were frosting the cake.

Frosting

Boil for a couple of minutes:

 1 stick margarine

4 tablespoons cocoa powder

1/2 cup buttermilk

Place 1 box powdered sugar in mixing bowl, pour boiling mixture over top, add 1 tsp vanilla and mix with electric mixer until you see it start to hold just a little shape.  It will be runny and you will pour it over the top of the peanut butter on the cake. 

Cover tightly with foil and refrigerate. 

1/2 cup buttermilk

I've made this cake for 35 years and still cannot guarantee that the frosting will set up.  I think it has to do with how long you boil the liquid and how much you mix with mixture.  I've recently learned to blend it longer before pouring on cake.  It will always be "pourable" tho.  Even if the frosting is gooey, it's still a big hit.  Must be served with vanilla ice cream and a big glass of cold milk.

Enjoy and let me know how you liked it.

Nancy