Preheat oven to 350 degrees Fahrenheit. Line sheet trays with parchment paper or a silicone baking mat.

Whisk together the flour, instant pistachio pudding mix, baking soda and salt in a large bowl. Set aside.

Cream together the butter, granulated sugar, and brown sugar in an electric mixer with the paddle attachment until light and fluffy.

Add the egg, vanilla extract, and green food coloring. Mix until incorporated.

Add the dry ingredients to the wet ingredients in the mixer. Mix until just combined.

Gently mix in the white chocolate chips and pistachios.

Use a cookie scoop (a #40 or #30 scoop; about 1 1/2 to 2 Tablespoons) to scoop dough balls onto prepared sheet trays about 2 to 3-inches apart. You may want to round this cookie dough in your hand before placing it on the baking sheet, to help the nuts and white chocolate chips stay tucked inside.

Bake the cookies at 350 degrees Fahrenheit for 10-12 minutes. The edges and bottoms should be light brown. Allow cookies to rest on the tray for a few minutes before transferring them to a wire rack to cool completely.