Put the mixture on the fire and bring to a boil. Keep stirring and cook for a few minutes, until it starts to thicken.
Put the fire off and stir in the orange blossom water.
Pour into 6 small to medium glasses and refrigerate for at least 6 hours (better overnight).
An hour before serving, prepare the citrus salad.
Segment the citrus. Using a sharp knife, carefully slice off the top and bottom of the fruit. Slice the skin away from the flesh and discard. Remove any remaining white pith. Cut between the membranes to segment the citrus. Cut the bigger pieces in half. Keep any juices aside.
In a bowl, mix the cut citrus, its juices, the raisins, pistachios and mint leaves.
Top the Biancomangiare with the citrus salad. Serve immediately.