Heat oven to 350 degrees F. Grease a 9 x 13-inch pan, and set aside.
Combine the flour, oats, baking soda and salt in a small bowl.
In a medium bowl, cream the butter, sugar and brown sugar together until
Add the egg, vanilla extract and 1/2 cup of the peanut butter and mix
Fold the dry ingredients into the wet mixture. Mix until just combined.
Spread the dough into prepared pan.
Bake for 20 minutes, until lightly golden brown.
Remove the crust from the oven and immediately sprinkle on the chocolate
chips. Wait for a minute or two, then spread them evenly across the dough as
While the chocolate is melting, combine in a separate bowl the confectioners'
sugar, remaining peanut butter and evaporated milk. Beat together and spread
onto the melted chocolate, forming a marbled pattern.