milk (may need more depending on consistency)
In a large bowl, mix together sugar, baking soda, flour and salt. Set aside.
Combine butter, water and peanut butter in saucepan and bring to a boil. Pour over flour mixture.
Add milk, vanilla and eggs. Mix. Pour in large cookie sheet or jelly roll pan. Bake at 400º for 20 minutes.
Frosting: Bring butter, peanut butter and milk to a boil in saucepan. Add powdered sugar. Pour warm frosting over cooled cake.