Cream butter and sugars.
Add egg and blend.
Add peanut butter, baking soda, salt, vanilla, flour and oatmeal.
Spread into a greased and floured 13x9x2" pan.
Bake at 325° for 20-25 minutes.
Remove from oven and immediately sprinkle with a 6-ounce package of chocolate chips. Let stand until melted and then spread evenly over the cake.
For topping, mix powdered sugar, peanut butter and milk. Add more milk to get desired consistency. When cool, spread this topping over the chocolate chips.