Preheat the oven to 325 degrees F (165 degrees C). Grease a 10x15 inch jellyroll pan.
In a large bowl, cream together the butter, white sugar and 3/4 cup peanut butter until smooth. Beat in the eggs one at a time, then stir in the vanilla. Combine the flour, baking soda and salt; stir into the peanut butter mixture. Mix in the oats until evenly distributed. Press the dough evenly into the prepared pan.
Bake for 10 to 12 minutes in the preheated oven. Remove from the oven and sprinkle the chocolate chips evenly over the top. Return to the oven for 2 more minutes, or until chocolate chips are shiny. Remove and spread the chips out smooth. Set aside to cool. In a small bowl, mix together the remaining peanut butter, confectioners' sugar and evaporated milk until smooth. Spread over the chocolate layer when cool. Cut into bars.