Preheat oven to 325°F (165°C) and grease an 8x8 inch square baking pan with parchment paper.

In a medium mixing bowl, combine melted butter and 1 cup sugar until smooth. Whisk in 2 eggs and vanilla extract.

Sift together cocoa powder, flour, and salt. Fold into the wet brownie mixture until just incorporated.

Spread the brownie batter evenly into the prepared baking pan, reserving 1/4 cup of batter for the marble effect.

In a separate bowl, beat softened cream cheese and 1/4 cup sugar until creamy. Incorporate 1 egg and pistachio paste until smooth.

Spread the pistachio cream cheese mixture over the brownie base. Drop small spoonfuls of the reserved brownie batter on top.

Use a clean knife or skewer to gently swirl the layers together to create a marbled pattern.

Evenly distribute chopped pistachios over the surface.

Bake for 30 to 35 minutes until the edges are set but the center remains slightly tender.

Allow the pan to cool completely to room temperature before refrigerating for at least 2 hours to ensure clean slicing.