Place the butter in a medium saucepan over medium heat. Stir as it melts and begins to foam. Continue cooking until the butter turns golden and small brown bits form on the bottom, giving off a nutty aroma, about 6 to 8 minutes. Remove from heat and pour into a heat-safe bowl. Let it cool for 5 to 10 minutes until warm but not hot.

In a mixing bowl, stir together the brown butter and brown sugar until smooth. Add the egg, egg yolk, and vanilla extract, mixing until fully combined.

Stir the pistachio cream into the batter until evenly blended.

Gently mix in the flour and salt just until no dry streaks remain. Fold in the chocolate chips and chopped pistachios.

Preheat the oven to 350°F. Line or lightly grease an 8×8-inch light-colored baking pan. Spread the batter evenly into the pan.

Spoon small dollops of pistachio cream over the surface and lightly swirl with a knife. Sprinkle extra chocolate chips and pistachios on top if desired. Bake for 20 to 25 minutes, until the edges are lightly golden and the center is set but still soft.

Allow the blondies to cool completely in the pan before slicing for clean, even squares.