Line an 8x8 inch pan with foil and then grease it with cooking spray.
Microwave butter to melt it.
Add the 2 cups of chocolate chips and the ½ cup of peanut butter into the bowl with the butter.
Microwave the mixture for 1 minute and then 15 second intervals until completely melted, stirring between microwaving.
Whisk in eggs, sugar, and vanilla until smooth.
Whisk in cocoa powder until smooth.
Pour batter into the pan.
Bake for 40-45 minutes.
Let cool.
For Drizzle:
Melt the chocolate chips completely. Drizzle over brownies using a piping bag, a ziplock with a corner clipped off, or a spoon.
Heat the peanut butter for 30 seconds. Don't melt it, just soften it. Drizzle the peanut butter in the same manner as the chocolate but perpendicular to the chocolate drizzle.
Recipe by Birch Tree Baking at https://www.birchtreebaking.com/flourless-peanut-butter-chocolate-fudge-brownies/