In a stand mixer, cream butter with sugars. Add ½ cup peanut butter, egg, vanilla & skim milk. Combine & scrape bowl.
Add baking soda, baking powder & flour all at once. Mix until just combined. Fold in HALF of the bag of Heath bits, & HALF of the bag of Reese's chips.
Bake at 350˚F for 18-24 minutes or until edges & top are browning (mine took 21 minutes.) Let cool completely about 1 hour.
In a large bowl combine chocolate chips & remaining peanut butter chips. Microwave for 2 minutes, stirring every 30 seconds, or until melted. Add ¼ cup peanut butter & stir until combined. Spread evenly over the top of the cooled cookie bars. Sprinkle immediately with remaining toffee bits & press down lightly. Let set in refrigerator for 30 minutes. Cut & serve.
Extra tip: If the edges of the cookie layer are a little higher than the center after it cools down go ahead & trim them. It will make your chocolate layer spread nice & flat. Just munch on the scraps :)