Preheat oven to 350 degrees ℉ and spray a jelly roll pan (17.8 x 12.8 x 1 inch) with nonstick cooking spray or line with parchment paper.
In a large mixing bowl, cream together butter, sugar and brown sugar together.
Add the vanilla, eggs, and 1 cup of the peanut butter. Mix well
Add oats, flour, baking soda and salt and mix until well combined. Spread dough in an even layer onto the prepared pan. The dough will be wet so it helps to spray your hands with cooking spray to press it in.
Bake bars for 15 minutes and remove from oven.
Drop remaining 1 ½ cups of peanut butter in small spoonfuls all over on top of warm bars. Let peanut butter sit for about 5 minutes and spread when peanut butter has softened and melted. Let bars sit until set up before spreading the chocolate frosting on.
For the chocolate frosting: In a large bowl, beat together the butter, powdered sugar, cocoa, milk, and vanilla until smooth and spread on top of bars. Cut into bars and serve.