Preheat your oven to 350°F (175°C) and grease a 9x13 inch baking dish.
In a large mixing bowl, combine the cake mix, pistachio pudding mix, eggs, sour cream, vegetable oil, and milk.
Beat the mixture on medium speed for 2 minutes until well mixed.
Pour the batter into the prepared baking dish and smooth the top with a spatula.
Sprinkle the chopped pistachios evenly over the top of the batter.
Bake in the preheated oven for 45-50 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cake to cool completely in the pan before slicing and serving.