Peanut Butter and Chocolate Fudge Melt Away Cake

My mother surprised my cousin, Barbara, who loves peanut butter and chocolate with this cake for her birthday. When she took the first bite, she moaned and said, "Oh gosh, just be quiet and let me savor this." Everyone who tasted this new recipe absolutely vowed it to be A KEEPER. I hope you enjoy it.
1 cup butter
1/3 cup cocoa
1 cup water
1/2 cup buttermilk
2 eggs, beaten
2 cups sugar
2 cups all-purpose flour
1 teaspoon baking soda
1 teaspoon vanilla
3/4 tablespoon vegetable oil (peanut preferred)
1 cup peanut butter


Buttermilk Icing
1/4 cup cocoa
1/2 cup butter
6 tablespoons buttermilk
1 teaspoon vanilla
1 lb powdered sugar or more for desired consistency
Preheat oven to 350 degrees. Combine butter, cocoa, water, buttermilk, and eggs in a pan. Cook over low heat until bubbly. Add flour, sugar, baking soda, and vanilla. Mix well. Pour into nonstick 11x13-inch cake pan. Bake for 30 minutes. Mix the oil and peanut butter together and spread over warm cake. Chill thoroughly. Make icing by combining cocoa and butter in pan. Cook until bubbly. Add the remaining ingredients. Mix until spreading consistency.