Preheat your oven to 350°F (175°C). Grease a square baking pan (8x8 inches) or line it with parchment paper for easy removal of the brownies.
In a medium saucepan over low heat, combine the chopped bittersweet chocolate and cubed butter. Stir continuously until melted and smooth. Remove from heat and let it cool slightly.
In a large mixing bowl, whisk together the granulated sugar and slightly beaten eggs. Mix until well combined, then add in the melted chocolate mixture and vanilla extract.
Gently fold in the salt and all-purpose flour until just combined. Avoid overmixing to keep the brownies fudgy.
Pour the brownie batter into the prepared baking pan. Bake for 20-25 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs. Allow the brownies to cool completely in the pan.
In a mixing bowl, beat the softened cream cheese and creamy peanut butter until smooth. Gradually add the confectioners' sugar and vanilla extract, mixing until combined. If the mixture is too thick, add 2-3 tablespoons of heavy cream to achieve a spreadable consistency.
Once the brownies have cooled, cut them into small squares. In parfait glasses, layer brownie pieces, a dollop of peanut butter cream, chopped peanut butter cups, and repeat until you reach the top. Finish with whipped cream and sprinkle with chopped peanut butter cups and melted chocolate for decoration.
Refrigerate the parfaits for at least 30 minutes before serving. This allows the layers to set and the flavors to meld beautifully.