Prepare Dry Ingredients: In a medium bowl, whisk together the all-purpose flour, baking soda, and salt. Set aside.
Cream Butter and Sugars: In a large bowl, use an electric mixer to cream the room temperature butter, granulated sugar, and brown sugar together until the mixture is light and fluffy, about 2-3 minutes.
Add Egg and Vanilla: Beat in the egg and vanilla extract until thoroughly combined.
Combine Dry and Wet Ingredients: Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Overmixing at this stage can lead to tough cookies, so stop as soon as you see no more flour streaks.
Fold in White Chocolate Chips and Pistachios: Using a spatula, gently fold in the white chocolate chips and toasted pistachios until evenly distributed through the dough.
Chill the Dough: Cover the bowl with plastic wrap and refrigerate the cookie dough for at least 30 minutes. This chilling step helps prevent the cookies from spreading too much while baking.
Preheat Oven and Prepare Baking Sheets: Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper. This prevents sticking and ensures even baking.
Shape and Bake: Scoop tablespoon-sized balls of dough onto the prepared baking sheets, spacing them about 2 inches apart. Bake in the preheated oven for 10-12 minutes, or until the edges are lightly golden and the centers are set.
Cooling: Allow cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely. This step helps them set properly without breaking.