Preheat your oven to 350°F (175°C). Grease the 9x13-inch baking dish or line it with parchment paper for easy removal.
In a large mixing bowl, use an electric mixer to combine the softened butter and granulated sugar until creamy and light in color, about 2-3 minutes.
Add the egg and vanilla extract to the butter mixture, mixing until combined.
In another bowl, whisk together the flour, baking soda, salt, and pistachio pudding mix. Gradually add this dry mixture to the wet ingredients, mixing on low speed until just combined.
Pour the cookie batter into the prepared baking dish and spread it evenly using a rubber spatula.
Sprinkle the chopped pistachios on top of the batter, pressing them slightly into the surface.
Bake in the preheated oven for 25 minutes or until the edges are lightly golden and a toothpick inserted in the center comes out clean.
Allow the bars to cool in the baking dish for about 10 minutes before transferring them to a wire rack to cool completely.
Once cooled, cut into 12 bars and serve.