Preheat oven to 350°. Line a 9x9” pan with foil and spray with cooking spray.
Crush Oreo cookies to a fine crumb using a food processor. You can also place them in a gallon size ziploc bag and roll it gently with a rolling pin until you have a fine crumb. Stir cookies into melted butter and press into the bottom of your pan. Chill until brownies are prepared.
Place the two baking chocolates and butter in a large, microwave safe bowl. Heat on HIGH power for 2-3 minutes, stirring every 30 seconds, until chocolate is smooth. Stir in sugar. Add eggs, salt, vanilla, and cocoa and stir well. Add flour and stir carefully.
Spread batter in prepared pan. Sprinkle the top with the chopped peanut butter cups.
Bake about 31-34 minutes, until a toothpick 1 inch from the outside of the pan comes out mostly clean. The center may still be a little jiggly. Let cool before cutting.
Store in an airtight container at room temperature for up to 4 days, or place in an airtight container and freeze for up to one month.