Make the brownies:
Preheat your oven to 350°F (175°C). Grease or line an 8×8-inch square baking pan with parchment paper.
In a medium bowl, whisk together the melted butter and granulated sugar until smooth.
Add the eggs and vanilla extract, and mix until well combined.
In a separate bowl, sift together the flour, cocoa powder, baking powder, and salt. Gradually fold the dry ingredients into the wet ingredients until fully combined.
Stir in the chocolate chips (if using).
Pour the brownie batter into the prepared pan, spreading it evenly with a spatula.
Bake for 20-25 minutes, or until a toothpick inserted into the center comes out with just a few crumbs. The brownies should be set but still soft and fudgy in the center.
Remove the brownies from the oven and let them cool completely in the pan on a wire rack.

Prepare the peanut butter layer:
In a medium bowl, combine the creamy peanut butter, powdered sugar, softened butter, and vanilla extract.
Use a hand mixer or a spatula to mix everything until smooth and fully incorporated.
Once the brownies have cooled, spread the peanut butter mixture evenly over the top of the brownies. Use a spatula to smooth it out into an even layer.
Place the brownies in the refrigerator to chill for at least 30 minutes, allowing the peanut butter layer to firm up.

Make the chocolate ganache:
In a small saucepan, heat the heavy cream over medium heat until it just begins to simmer (do not let it boil).
Remove from heat and pour it over the semisweet chocolate chips in a heatproof bowl.
Let it sit for 2-3 minutes, then stir until smooth and glossy.
Allow the ganache to cool slightly before pouring it over the peanut butter layer on the brownies.

Finish the brownies:
Once the ganache has cooled slightly, pour it over the peanut butter layer, spreading it evenly to cover the entire surface.
Return the brownies to the refrigerator and chill for at least 1 hour, or until the ganache is set.

Serve:
Once the brownies have set, remove them from the refrigerator.
Cut into squares and serve chilled or at room temperature. Enjoy!