Combine the flour, sugar, salt, and baking soda in a large mixing bowl, and set aside. In a large saucepan, bring the peanut butter, water, and butter to a rapid boil. Pour it over the flour mixture, and mix well. Add the eggs and buttermilk. (If you don't have buttermilk, you can substitute sour milk: add 1 T. vinegar to the 1/2 c. milk) Pour into a greased sheet cake pan. Sprinkle the chocolate chips over the batter evenly. Bake at 350 degrees for 20-25 minutes, or until a toothpick comes out clean.

To make the frosting, bring the butter, peanut butter, and milk to a boil. Add the vanilla and powdered sugar, and mix well. I like to use a whisk to make sure all the little lumps of sugar get mixed in!

Cool the cake slightly, then frost while cake is warm.