In a large bowl, combine butter and peanut butter until smooth. Add sugars, vanilla, eggs, milk, salt, soda, flour and oatmeal. Press mixture into greased 6 by 9 and bake for about 20-25 minutes, or until puffed and browned.
Let the bars cool for a few minutes and then peanut butter on top. If you do it right away, it kind of squishes the bars. And I don't like squished bars.
After the bars have cooled for 10 minutes or so, combine butter and milk in a small saucepan over low heat until butter is melted. Stir in cocoa powder and powdered sugar. Spread gently on the top of the bars.