Preheat oven to 350°F (175°C). Line a 12-cup muffin tin with cupcake liners.
In a large mixing bowl, combine white cake mix, pistachio pudding mix, milk, oil, and eggs.
Mix on medium speed for about 2 minutes, scraping down the bowl halfway through, until smooth and fully incorporated.
Gently fold in the chopped pistachios until evenly distributed.
Using a large cookie scoop, fill cupcake liners about ⅔ full.
Bake for 18–20 minutes, or until a toothpick inserted in the center comes out clean.
Allow cupcakes to cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.
In a small bowl, stir together the vanilla frosting and finely ground pistachios until evenly combined.
Add frosting to a piping bag or baggie.
When cupcakes are completely cool, frost the cupcakes