Prepare: Set your oven to 350°F. Spray the inside of your 9x13-baking pan and line it with parchment paper, this helps the parchment stick to the pan and not slide all over. Optionally, you can also spray the parchment paper with non-stick spray for easy removal after baking.
Mix the brownie batter: Place the butter in a large microwave-safe mixing bowl, melt completely. Add the sugar, cocoa, vanilla, and eggs. Whisk to combine well.
Incorporate the dry ingredients: Add the flour, baking powder, and salt to the bowl and whisk until completely combined, but do not over mix. Fold in the milk chocolate chips.
Bake the brownies: Pour the brownie batter into the prepared pan, spreading it evenly. Bake for 25 to 28 minutes or until a toothpick inserted into the center comes out with a few moist crumbs.If it is wet, it is not done. If it is dry, it will not be moist and fudgy.
Cool the brownies: Let the brownies cool completely in the pan. Meanwhile prepare the peanut butter filling.
For the Peanut Butter Filling:
Prepare the filling: In a medium mixing bowl, beat together softened butter, creamy peanut butter, vanilla extract, powdered sugar, salt, and milk until smooth and creamy.
Spread the filling: Once the brownies are cool, spread the peanut butter mixture evenly over the top, creating a smooth layer.
For the Chocolate Ganache:
Create the ganache: In a microwave-safe bowl, combine chocolate chips and butter. Microwave in 15-second intervals, stirring in between, until the mixture is melted and smooth. Add heavy cream and mix until well incorporated.
Pour and spread the ganache: Pour the chocolate ganache over the peanut butter layer, spreading it evenly with a spatula.
Set and Serve:
Chill the brownies: Place the brownies in the fridge to allow the chocolate ganache to set for 30 minutes to an hour.
Slice and enjoy: Once set, lift the brownies out of the pan using the parchment paper overhang. Place them on a cutting board and slice into squares.
Notes
If your kitchen is warm, consider refrigerating the brownies after spreading the peanut butter mixture on them.For a glossy ganache, consider using oil instead of butter when melting the chocolate chips.Experiment with different nut butters like almond or cashew for unique flavor twists.