A lighter, more delicate biryani than Hyderabad's. The rice is perfumed with rose and kewra, the spice level is gentle, and the star of the show is the golden potato that absorbs all the meat juices. The boiled egg is non-negotiable.
When Nawab Wajid Ali Shah was exiled from Lucknow to Metiabruz in Kolkata in 1856, his khansamas (cooks) came with him. But meat was expensive in Bengal, so they substituted potatoes and added boiled eggs to stretch the portions. This accident became a signature — the Kolkata biryani's aloo is now its most fiercely defended element.
The potato. In every other biryani tradition, potato is a filler. In Kolkata, it's the main character. A properly cooked Kolkata biryani potato — soaked in meat fat, spiced with nutmeg and saffron — is worth more than the meat itself.
Mix mutton with yogurt, ginger-garlic paste, half the fried onions, all masala powders, and salt. Rest 2 hours minimum.
Boil eggs, peel, and lightly fry in oil until golden. Prick potatoes with a fork and fry until light golden on all sides. Set both aside.
In a heavy pot with ghee, cook the marinated meat on medium for 20 minutes until half-done. Add potatoes and eggs on top.
Cook soaked rice with whole spices until 70% done. Drain.
Spread rice over the meat. Drizzle saffron milk, kewra water, rose water, remaining fried onions, and ghee. Seal tightly. Cook on high 3 min, then lowest flame for 25 minutes.
Rest 10 min. Serve each plate with rice, 1-2 pieces of mutton, one whole potato, and half an egg. The potato must be intact.