In a medium bowl, gently whisk together the all-purpose flour, instant pistachio pudding mix, baking soda, and salt. Set this dry mixture aside.
In a larger mixing bowl, cream together the softened unsalted butter with both the light brown sugar and granulated sugar until the mixture is light and fluffy – this usually takes about 3 to 5 minutes.
Beat in the room temperature egg and clear vanilla extract until everything is well combined and smooth.
Gradually add the dry ingredient mixture to the wet ingredients, stirring until just combined. If you'd like a brighter green color, now's the time to gently mix in a few drops of food coloring.
Carefully fold in the white chocolate chips and chopped pistachios until they are evenly distributed throughout the dough.
Cover the cookie dough and chill it in the refrigerator for at least 30 minutes. This important step helps prevent the cookies from spreading too much, ensuring a perfect texture.
While the dough is chilling, preheat your oven to 325°F (160°C). Line a baking sheet with parchment paper for easy cleanup.
Scoop out rounded tablespoons of the chilled dough and roll them into neat balls. Place them about 2 inches apart on your prepared baking sheet.
Bake for 12 to 14 minutes, or just until the edges are lightly set and you see no browning. Keeping them slightly underbaked ensures a super soft and chewy cookie!
As soon as they come out of the oven, gently press a few extra white chocolate chips onto the top of each warm cookie for a beautiful finish.
Let the cookies cool on the baking sheet for a few minutes before carefully transferring them to a wire rack to cool completely. Enjoy these delightfully soft and flavorful treats!