Soak gelatine in cold water. Bring the milk, sugar and rose water to the boil in a saucepan and simmer over a low heat, stirring occasionally, for about 2 minutes. Stir starch with approx. 6 tbsp. water until smooth. Pour into the milk while stirring and let it simmer for about 2 minutes while stirring occasionally. Remove the pot from the stove.
Squeeze the gelatine, stir into the hot milk and dissolve in it. Chop the pistachios. Stir approx. 3/4 into the milk and fill 4 cups (each containing approx. 300 ml) with milk. Chill for about 2 hours.
Sprinkle milk pudding with remaining pistachios and decorate with petals.