Preheat your oven to 350 degrees. Line a 13x9" baking pan with parchment paper.
Whisk together flour, cocoa powder, salt and baking soda. Set aside.
Using a stand mixer, cream the butter, brown sugar and granulated sugars. Mix in 1 tsp vanilla and the 1 egg. Beat until smooth.
Carefully add in the dry ingredients and mix until completely combined.
Spread the cookie dough in the prepared baking pan. Bake for 18 minutes and no longer shiny. COOL COMPLETELY.
Mix peanut butter, powdered sugar and 1 tsp of vanilla until smooth. Spread over the COOLED cookie bars.
Place the dark chocolate chips and the vegetable oil in a bowl and heat on high in the microwave for 30 seconds at a time. Stir after each 30 seconds until smooth. Spread over the peanut butter layer in the pan. Sprinkle with chopped peanuts.
Let the cookie bars harden for a few hours or chill the bars in the refrigerator.
You can store these cookie bars in an airtight container for up to 5 days or freeze them for month.