Preheat the oven to 350 degrees. Line a 9x13 inch baking dish with foil or parchment paper and grease.

Brownie Batter - Combine butter and 2 ounces chocolate to a microwave safe bowl. Microwave on 30 second intervals, stirring after each interval until melted and smooth. This takes me about 1 minute and 30 seconds.

In a medium bowl, combine melted chocolate mixture and sugar, whisking until completely combined. Add vanilla extract and eggs then whisk until smooth. Stir in the cocoa powder, flour and salt until smooth and just combined, try not to over mix the batter. It will be thick. Stir in remaining chocolate chips/chunks. Melt peanut butter in microwave safe bowl and add 1/4 cup of the melted peanut butter (you will use the remaining 1/4 cup later) and gently stir, leaving a few streaks of peanut butter; set aside.

Oatmeal Cookie - In a large mixing bowl or bowl of a stand mixer, add the oatmeal, flour, brown sugar, baking soda, salt, oil, egg and vanilla and beat until combined and the dough holds together (the dough will seem oily, this is good, if not add a tablespoon more of oil). Fold in about 1/2 cup of the chocolate chunks.

Assemble - Drop dollops of about half the brownie batter into the prepared pan (see images below). Sprinkle 3/4 of the oatmeal cookie dough around and over the brownie batter and in the corners. Dollop the remaining brownie batter over top the oatmeal cookie dough. Remelt peanut butter in microwave and swirl into brownie batter dollops, using a knife to swirl it. Drizzle any remaining over entire pan. Slightly press a handful of chocolate chunks into the top of batter.

Bake for about 25-35 minutes, just do not over bake. Cover with foil the last 10 minutes to ensure the top does not get crispy. Allow bars to cool in pan for at least 1 hour before slicing and serving.