Line a large sieve with a double layer of paper towels. Place a bowl under the sieve and pour the yogurt into the sieve. Refrigerate for as long as possible to allow the liquid to drain off the yogurt. This will take a minimum of 5 to 6 hours.
Heat a little milk in a small pan. Place two teaspoons of the milk into a small bowl and crumble the saffron strands into it (the rest of the milk can be used in another dish). Allow the saffron to infuse the milk for about 10 minutes using the back of a spoon to crush the saffron further into the milk.
Remove the yogurt from the refrigerator (the liquid in the bowl below can be discarded). Transfer the yogurt to a medium mixing bowl. Sift the sugar into the thickened yogurt, then add the saffron milk and ground cardamom. Cover the bowl, and chill in the refrigerator.
To serve, divide the yogurt among 4 bowls and garnish with the nuts, silver leaf, if using, and pomegranate seeds.