Soak the Basmati rice for half an hour. Boil it with a bay leaf and a teaspoon of salt until it is 80% cooked. It should be grainy when mashed between fingers.
Deep fry the sliced onions until golden brown and keep aside.
In the same oil, deep fry the paneer and the potato cut into cubes until they colorize.
Heat 3 tbsp of oil in a flat bottom pan. Use the same oil you fried the onions in for extra flavor. Add in a bay leaf and a tsp of cumin seeds (jeera).
Add the whole garam masala. When it starts to crackle, add in one small onion sliced and saute until it changes color.
Add in the ginger garlic paste. Saute for a minute. Add in the chopped green chillies and cook.
Add in the mixed vegetables and saute.
Add in the cumin powder (jeera), coriander powder (dhania), fennel powder (saunf), salt, Kashmiri red chilli powder, and turmeric powder. Mix well.
Add in the curd. Mix well. Add in the potatoes. You can add a bit of water so that the masala does not burn. Add in the lemon juice.
Add the fried paneer pieces. Save some paneer pieces for the top layer. Mix well. Check the salt and add more if required.
To arrange, first switch off the flame. Top the vegetables with half of the fried onions, chopped coriander leaves and mint leaves. Save some for garnish. Cover it with the boiled rice.
Top the rice with the fried onions, mint leaves, coriander leaves, and the remaining paneer pieces. Add a tablespoon of the onion flavored oil and kewra essence.
Cover it with a lid. Switch on the flame and cook on high for 2-3 minutes. Reduce the heat and cook for 3-4 minutes.
Switch off the flame and let it rest for 5 minutes. Remove the lid and fluff the rice with a fork.
The Subz Biryani is ready to serve. Garnish with lemon slices and chopped coriander leaves, mint leaves, and the fried onions. Serve with dahi tadka.