01 - Preheat oven to 350°F. Line a 12-cup muffin tin with paper liners.
02 - Process 4.25 oz pistachios in a food processor until finely ground. Reserve 1-2 tbsp for garnish.
03 - Sift flour, baking powder, and salt into a bowl. Stir in ground pistachios until evenly distributed.
04 - Beat butter and sugar in a large bowl until light and fluffy, approximately 3 minutes.
05 - Incorporate eggs one at a time, mixing thoroughly after each addition. Blend in vanilla extract.
06 - Add dry ingredients in two portions, alternating with milk, beginning and concluding with flour mixture.
07 - Distribute batter uniformly among prepared cupcake liners.
08 - Bake for 18-20 minutes until a toothpick inserted into the center emerges clean. Allow to cool completely.
09 - Finely grind 3.5 oz pistachios for the frosting, leaving slightly coarse if texture is preferred.
10 - Whip butter until smooth and creamy. Gradually incorporate powdered sugar, beating until fully combined.
11 - Fold in ground pistachios, vanilla, salt, and 2 tbsp milk. Whip until fluffy, adjusting consistency with additional milk if necessary.
12 - Pipe or spread buttercream over cooled cupcakes. Garnish with reserved ground pistachios.