Place a mesh strainer in a large bowl. Line a cheesecloth over the strainer. Pour the yogurt onto the cheesecloth, gather the corners of the cloth and tie into a bundle. Now you can either hang this cheesecloth or place a heavy weight on top of it.
We want to leave space for the water to collect in the bowl. Leave it out (3-4 hours) or leave it overnight in the refrigerator. For greek yogurt, straining 3-4 hours is enough. If using plain yogurt, strain at least overnight or upto 24 hours in the refrigerator.
Add saffron to warm milk and keep aside. Remove and empty the thickened yogurt in a large bowl. Whisk it well for 3-4 minutes to make it smooth.
Add the mango pulp (see notes for how to make pulp from fresh mangoes), sugar, cardamom and saffron soaked in milk. Mix for 3-5 minutes until combined and smooth without any lumps.
Chill for 1-2 hours before serving. Serve in bowls and garnish with crushed pistachios and some saffron strands.