In a medium bowl, whisk together the flour, dry pudding mix, baking soda, and salt. Set aside.

In a large bowl using a hand mixer or stand mixer with a paddle attachment, cream the softened butter, granulated sugar, and brown sugar together on medium speed for 2-3 minutes, until light and fluffy.

Add the eggs one at a time, mixing well after each addition. Mix in the vanilla extract.

With the mixer on low speed, gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Using a spatula, gently fold in the white chocolate chips and chopped pistachios.

Cover the bowl and chill the dough in the refrigerator for at least 1 hour (up to 24 hours).

Preheat oven to 350°F (175°C). Line baking sheets with parchment paper.

Scoop 1.5-tablespoon portions of dough onto the prepared baking sheets, spacing 2 inches apart.

Bake for 10-12 minutes, until the edges are just set but the centers still look soft. Do not overbake.

Let the cookies cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.