In a large mixing bowl, cream together butter, brown sugar, granulated sugar and peanut butter. Add eggs and vanilla. Add soda and salt and mix until well blended. Add flour slowly, making sure it’s incorporated, but do not overmix. Stir in oatmeal by hand.
Spray a 15 x 10 jelly roll pan with nonstick cooking spray. Spread mixture in a pan. (I wet my hand slightly and press the mixture evenly.) Cook at 350 degrees for 12 – 15 minutes until golden brown.
Remove from oven and immediately drop peanut butter (from the topping ingredient list) by teaspoonfuls evenly around the top. Allow to melt and spread smooth with a spatula.
Allow to cool thoroughly.
In a small saucepan, bring sugar, evaporated milk, and butter to a full boil for 45 seconds. Remove from the heat and add the milk chocolate chips. Whisk until chocolate sauce is smooth. Pour evenly over bars and allow to set before cutting and serving.