Prepare the Brownie Base

1. Preheat your oven to 350 °F (175 °C). Generously grease an 8​-inch square baking pan.
2. Place the chopped bittersweet chocolate and butter into a microwave-safe bowl. Heat at half power in 30​-second intervals, stirring until the butter is melted and the chocolate becomes smooth. Let the mixture cool slightly.
3. In another bowl, whisk together the granulated sugar, brown sugar, egg, vanilla extract, and salt until combined.
4. Stir in the melted chocolate mixture. Mix just until combined.
5. Add the flour, folding in gently until just incorporated.
6. Spread the batter evenly in the prepared pan.
7. Bake for 15–20 minutes, or until a toothpick inserted into the center comes out with moist crumbs attached.
8. Cool the pan completely on a wire rack before proceeding.

2. Make the Peanut Butter Pie Filling

1. Using an electric mixer on medium speed, blend the cream cheese, creamy peanut butter, sifted confectioners’ sugar, and vanilla extract until smooth and well combined.
2. In a separate bowl, whip the heavy cream with a whisk attachment until soft peaks form.
3. Gently fold the whipped cream into the cream cheese–peanut butter mixture, being careful not to overmix.

3. Assemble & Chill

1. Evenly layer the peanut butter mixture over the completely cooled brownie base.
2. Refrigerate for about 4 hours, or until firm and set.
3. Slice into bars and serve chilled. Keep leftover bars refrigerated.