• Preheat oven to 350F.
• Lightly spray an 9-inch square baking pan with cooking spray. Line with parchment paper leaving an overhang for easy removal. Set aside.

Peanut Butter Filling

• In a medium bowl, combine peanut butter, sugar, and egg. Mix until throughly combined. Set aside.

Brownies

• In a large bowl, combine chocolate chips and butter. Melt in 30-second increments, on high heat in the microwave, stirring in between.
• Stir in sugar and vanilla until completely combined.
• Add eggs one a time, stirring in between until combined.
• In a small bowl, whisk together cocoa powder, cornstarch, and salt.
• Add dry mixture to wet mixture and stir vigorously until the mixture is smooth and begins to pull away from the sides of the bowl. This will take one or two minutes.
• Stir in the mini chocolate chips.
• Pour two-thirds of the brownie batter into the prepared pan and smooth the top with a spatula.
• Drop small spoonfuls of the peanut butter mixture on top of the brownie batter.
• Spoon on remaining brownie batter and smooth with the back of a spoon or offset spatula. It doesn't have to be perfect.
• Bake for 33-37 minutes or until an inserted toothpick comes out with a few moist crumbs. (Watch the brownies closely after 30 minutes. Don't rely on the time so much as the inserted toothpick.)
• Let brownies cool completely on a cooling rack or in the fridge.

Ganache

• Place bittersweet chocolate in a heat-proof bowl.
• Heat whipping cream until scalding hot and pour over the top of the chocolate.
• Let sit for 5 minutes and then stir until smooth. (If chocolate hasn't melted all the way, heat on high heat in 15 second intervals in the microwave, stirring in between, until chocolate is fully melted.)
• Pour mixture over the top of the cooled brownies and use an offset spatula to spread over the top until smooth. Refrigerate until the ganache has completely set up.
• Cut into bars and serve.
• Store in an airtight container in the refrigerator.
• Use the parchment paper overhang to pull the brownies out and cut into squares.
• Store in an airtight container for up to 3 days.