- Preheat the oven to 350°F (175°C) and grease a 9x13-inch baking pan or line it with parchment paper.

- In a medium saucepan over low heat, melt the butter. Remove from heat and stir in the granulated sugar, brown sugar, and cocoa powder until smooth.

- Whisk in the eggs, one at a time, ensuring each is fully incorporated before adding the next. Stir in the vanilla extract.

- Add the flour and salt, mixing just until combined. Do not overmix.

- Spread the brownie batter evenly into the prepared pan and bake for 25–30 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.

- Allow the brownies to cool completely in the pan.

- In a large mixing bowl, beat the peanut butter and softened butter together until smooth and creamy.

- Gradually add the powdered sugar and mix well.

- Stir in the vanilla extract and add milk, one tablespoon at a time, until the mixture is spreadable but not too thin.

- Spread the peanut butter mixture evenly over the cooled brownies. Chill in the refrigerator while you prepare the ganache.

- In a microwave-safe bowl or a small saucepan, heat the heavy cream until steaming (but not boiling).

- Pour the hot cream over the chocolate chips and let it sit for 2-3 minutes.

- Stir the mixture until smooth and glossy.

- Pour the ganache over the peanut butter layer, spreading it evenly with an offset spatula.

- Refrigerate the assembled bars for at least 2 hours, or until the layers are set.

- Once chilled, cut into squares or rectangles. Use a sharp knife for clean cuts, wiping it with a warm, damp cloth between slices.