Preheat oven to 350 degrees. Use parchment paper or a silpat mat to line a baking sheet. Cream the butter, sugar and brown sugar in a stand mixer until light and fluffy (about 2-3 minutes). Scrape the sides of the bowl to make sure all ingredients are blended.
Add in egg and vanilla and beat until combined.
Add in flour, dark cocoa, baking soda and salt. Mix until the flour is ALMOST mixed in.
Add in 1 3/4 cup peanut butter chips and the Oreo chunks. (Save the remaining 1/4 cup of peanut butter chips for the drizzle)
Continue mixing until the dough is just combined. DON'T OVERMIX.
Scoop out dough and roll into balls. Scoop out a little less than 1 TBSP dough for smaller cookies (or 1/4 cup dough for BIG cookies). Place dough balls on prepared pan (12 cookies to a pan if smaller cookies) and slightly flatten with your hand to about 3/4 – 1 inch thick.
Bake at 350 degrees for 8-10 minutes. When the cookies no longer glossy in the middle, you can take them out of the oven.
Let the cookies cool on the pan.
Microwave the remaining 1/4 cup peanut butter chips for 45 seconds. Stir. Heat until completely melted.
Put the melted peanut butter chips in a small zip loc bag and cut the corner so that you can drizzle the peanut butter on top of the cookies.