Preheat your oven to 350°F (175°C) and prepare an 8x8-inch baking dish by greasing it lightly.

In a large mixing bowl, combine softened unsalted butter, brown sugar, and granulated sugar. Beat until light and fluffy, about 2-3 minutes.

Add the eggs one at a time, mixing on low speed, followed by the vanilla extract and pistachio pudding mix until smooth.

In a separate bowl, whisk together all-purpose flour, baking soda, and salt. Gradually add to the wet ingredients, mixing until combined.

Fold in chopped unsalted pistachios and white chocolate chips until evenly distributed.

Pour the batter into the prepared baking dish, smoothing the top. Bake for 25-28 minutes, until edges are golden and a toothpick comes out with a few moist crumbs.

Allow to cool in the pan for at least 30 minutes before slicing into squares and serving.