Step 1: Preheat your oven to 350°F (175°C). Line baking sheets with parchment paper.
Step 2: In a large bowl, cream together the softened butter, granulated sugar, and brown sugar with an electric mixer until light and fluffy (about 2-3 minutes).
Step 3: Beat in the eggs one at a time, mixing well after each addition. Stir in the vanilla extract and any optional green food coloring until fully combined.
Step 4: In a separate medium bowl, whisk together the all-purpose flour, instant pistachio pudding mix, baking soda, and salt.
Step 5: Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix.
Step 6: If using, gently fold in the white chocolate chips or chopped pistachios.
Step 7: Drop rounded tablespoons of dough onto the prepared baking sheets, leaving about 2 inches between cookies.
Step 8: Bake for 10-12 minutes, or until the edges are lightly golden and the centers are set but still look soft. Do not overbake.
Step 9: Remove from the oven and let cool on the baking sheets for 5 minutes before transferring to a wire rack to cool completely.