Preheat your oven to 350°F (175°C). Grease and line the bottom of a 9x13 inch baking pan with parchment paper, leaving an overhang on the sides for easy removal.

In a large mixing bowl, cream together the softened butter, granulated sugar, and brown sugar using an electric mixer or whisk until the mixture is light and fluffy, about 2-3 minutes.

Add the eggs one at a time to the butter and sugar mixture, beating well after each addition. Stir in the vanilla extract until well combined.

In another bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt. Gradually add the dry ingredients to the wet mixture, mixing until just combined. Do not overmix.

Gently fold in the chopped pistachios and white chocolate chips (if using) with a rubber spatula or wooden spoon until evenly distributed.

Pour the cookie dough into the prepared baking pan and use the spatula to spread it evenly.

Bake in the preheated oven for 25-30 minutes, or until the edges are light golden brown and a toothpick inserted in the center comes out clean.

Allow the cookie bars to cool in the pan for about 10 minutes, then lift them out using the parchment paper overhang and place on a wire rack to cool completely.

Once cooled, cut into 12 bars and serve. Enjoy!