Preheat your oven to 350°F (175°C). Line an 8×8 inch baking pan with parchment paper.
Mix the melted butter and sugar until smooth, then add the eggs and vanilla. Add the cocoa powder, flour, and salt, folding gently until everything is incorporated.
Spread the batter evenly into the prepared pan and bake for about 20–22 minutes. Let the brownie base cool completely.
In a medium bowl, beat the creamy peanut butter and softened butter until smooth and fluffy. Gradually add the powdered sugar and mix in the vanilla extract.
Spread the peanut butter layer evenly over the cooled brownie base and refrigerate for about 20 minutes.
Melt the chocolate with either the butter or the heavy cream. Pour the chocolate topping over the peanut butter layer and smooth it out.
Chill the entire pan for at least 1 hour. For perfect slices, use a warm knife to cut.