In a pot over medium heat, combine the milk, fine semolina, and sugar. Stir constantly until the mixture boils and thickens. Add orange blossom water or mastic, then pour the mixture into a large dish or individual cups.

For the second layer, bring the milk to a boil, then add the vinegar. When the milk curdles and separates, strain it and let it cool. Whip the crème fraîche until it doubles in volume, then add the curds and whip again. Spread this cream layer over the cooked semolina layer.