Preheat oven to 350 degrees. Line an 8x8 inch pan with foil or parchment and grease with nonstick spray.
Melt the butter, 2 cups chocolate chips, and 1/2 cup peanut butter in a microwave safe bowl at 1/2 power for 2 minutes. Stir until smooth (return to microwave for another 20 seconds at a time as needed until completely melted and smooth).
Add chocolate mixture to a large mixing bowl. Add eggs, sugar, cocoa powder, vanilla, and salt and mix until smooth. Transfer mixture to prepared pan and bake for 30-40 minutes until set and an inserted toothpick comes out mostly clean. Allow to cool completely.
Once brownies have cooled, melt remaining 1/4 cup chocolate chips and 1/4 cup peanut butter in a microwave safe bowl at 1/2 power for about 1 minute or until you can stir it smooth. Drizzle over cooled brownies. Place in the fridge for about 10 minutes for the drizzle to set. Cut into bars and serve.
Store in airtight container at room temperature up to five days.