Soak Saffron in warm milk for 10 minutes. The milk will turn pale yellow. You can also add a few drops of food color to the milk.
Take a large pot and coat it with ghee.
Place one-third of the cooked mutton in the bottom, followed by rice, fried onions (beresta), a few potato halves, and a boiled egg. In this layer, add a little saffron milk.
Add a similar layer on top of this by layering cooked mutton, fried onions, rice, potatoes, boiled egg, and saffron milk.
Finally, add kewra water and meetha attar to the top layer.
Close the lid and seal the edges of the pot with wheat flour dough.
Cook for 2 minutes on high heat and remove the pot from the heat.
Place an iron skillet on the heat and keep the biryani pot on top.
Keep the gas on low heat for around 10 minutes and later turn off the heat and set aside for 10 minutes.
Unseal the edges and serve the hot Kolkata style mutton biryani with raita.