Soak the saffron in the hot milk for at least 30 minutes. Heat a heavy frying pan and toast the pistachios with 1 tablespoon of the butter for 2 minutes, until they are lightly toasted but still green. Remove as much skin as you can from them and set aside. Dissolve the sugar in the milk over low heat and keep the mixture hot. Melt the remaining butter in a heavy saucepan, add the semolina, and cook, stirring, over low heat for about 8 to 10 minutes. Stir the saffron milk into the hot sugared milk and add to the semolina, and cook, stirring vigorously. Remove the helva from the fire, cover, and allow to stand in a warm spot for 15 minutes. Fold in the pistachios and serve warm or at room temperature in bowls.