Combine pistachio, sugar, and rose water together in a small bowl and mix well. Set aside.
Preheat oven to 325 degrees Fahrenheit and line a couple of cookie sheets with parchment paper.
Process flour with butter in a food processor until they are well combined. Sprinkle with rose water and milk. Continue processing until dough just forms a ball.
Dust maamoul molds well with flour. Invert and tap gently to remove excess flour. Estimate the amount of dough need to fill maamoul mold and make a ball of dough then divide remaining dough in to same-sized pieces and roll each into a ball. Flatten a ball out slightly and place a good tablespoon of filling in center. Close dough around filling to cover it. Pack ball into mold. Level off cookie even with the lip of the mold. Be sure you have not revealed filling or it will stick to the pan as it bakes.
Tap cookies out onto the work area with a sharp firm hit to the top of the mold. Transfer cookies to baking sheet with a spatula. Bake cookies for 12 -15 minutes until cooked through but not browned. Remove from pan and place on cooling racks.
Dust with powdered sugar before serving.