In a heavy based pan, place the milk over low heat. Stir occasionally for 1 hour until the milk reduces its original volume by 1/6th.
Roast the pistachio nuts and chop them.
Then combine the water & sugar. Heat them to make a thick syrup. Keep covered and warm.
Now add the sugar syrup, roasted pistas, rose-water and green coloring to the reduced milk. Stir until the mixture holds together without sticking to the pan.
Spread the mixture in a greased tray. Let it stand for about 45 minutes to set, then cut into squares.