Preheat oven to 375 degrees.
In a large bowl cream butter, peanut butter, brown sugar and sugar until smooth
Add 2 tablespoon of mixed egg, vanilla and mix until combined.
Put the rest of the dry ingredients into the creamed mixture and mix until all dry ingredients are incorporated.
Line an 8x8 square pan or a ⅛ cookie sheet pan with parchment paper. Spread the cookie batter evenly and bake in the middle rack of the oven for 18 to 20 minutes. The sides should be golden brown, and the middle should slightly rise.
Once you've taken the peanut butter bars out of the oven bang the pan on a heat safe surface to create beautiful lips on the sides and to create a dense bar in the middle.
While the peanut butter bars are still hot spread the peanut butter on top of the bars and spread. Allow the peanut butter bars to cool and make the chocolate icing.
In a small saucepan melt the butter and add cocoa powder. Mix until the cocoa powder clumps are gone. Take the pan off the stove and add in the powdered sugar, milk and vanilla and mix until it all comes together. There will be clumps of cocoa powder and powdered sugar, but continue to whisk until it blends in. I used a hand mixer and mixed until the clumps were gone.
Once the bars have cooled down pour the chocolate icing on top and spread. Allow the chocolate icing to set up before cutting and serving.
Store them in an airtight storage container for 5 to 7 days. I find that the peanut butter chocolate bars taste best the next day once the bars have set and cooled.