01 - Preheat oven to 350°F. Line a 12-cup muffin tin with paper liners.
02 - Finely grind 4.25 oz pistachios in a food processor. Reserve 1-2 tbsp for garnish.
03 - Sift flour, baking powder, and salt into a bowl. Stir in the ground pistachios.
04 - Beat butter and sugar in a large bowl until light and fluffy, approximately 3 minutes.
05 - Add eggs one at a time, beating thoroughly after each addition. Mix in vanilla extract.
06 - Add dry ingredients in two batches, alternating with milk, beginning and ending with flour mixture.
07 - Divide batter evenly among the prepared cupcake liners.
08 - Bake for 18-20 minutes until a toothpick inserted in the center emerges clean. Allow to cool completely.
09 - Grind 3.5 oz pistachios finely, leaving slightly coarse texture if desired.
10 - Beat butter until smooth and creamy. Gradually add powdered sugar, beating until fully incorporated.
11 - Mix in ground pistachios, vanilla, salt, and 2 tbsp milk. Beat until fluffy, adding additional milk as needed for consistency.
12 - Pipe or spread buttercream onto cooled cupcakes. Sprinkle with reserved ground pistachios.