Preheat the oven to 350ºF. Line a 12 cup muffin tin with paper liners. Set aside.
Place ¼ cup shelled pistachios in a food processor and grind until small and almost powdery. Watch carefully to prevent them from getting too sticky.
In a large bowl, whisk together flour, ground pistachios, sugar, baking powder, baking soda, cardamom, and salt.
Add buttermilk, rosewater, butter, egg, and vanilla extract and stir gently with a wooden spoon or rubber scraper until completely incorporated. The batter may still be a little lumpy, but you don’t want big dry lumps and you don’t want to overmix the batter.
Divide the batter evenly amongst the prepared muffin cups. Sprinkle the tops with dried rose petals, chopped pistachios, or any other topping you might want.
Bake 18-22 minutes or until the tops are firm and lightly browned, and a toothpick inserted in the center of one comes out clean. Allow to cool 10 minutes in the pan before removing to a wire rack to cool completely.