1. In a blender, puree the spinach leaves, 1/2 cup coriander, 1/2 cup mint, green chillies, and almonds with a splash of water into a smooth green paste; set aside.
2. Steep saffron strands in 1/2 cup warm milk. Squeeze excess water thoroughly from the soaked soy chunks.
3. In a large pot, bring 8 cups of water to a rolling boil with 1 inch cinnamon, 1 cardamom pod, 1 clove, and salt. Add soaked basmati rice and cook until 70% done (about 5-7 minutes). Drain and set aside.
4. Heat oil in a pan and deep-fry or shallow-fry the 2 cups of sliced onions until golden brown and crisp (birista); drain on paper towels.
5. In a heavy-bottomed pot, heat 2 tablespoons of oil and 1 tablespoon of ghee. Add cumin seeds, 2-inch cinnamon stick, 3 green cardamoms, black cardamom, 3 cloves, bay leaf, ajwain, and mace.
6. Add chopped onions and sauté until translucent. Stir in ginger-garlic paste and sauté until the raw aroma disappears.
7. Add chopped tomatoes, turmeric, red chilli powder, coriander powder, garam masala, and salt. Cook until tomatoes soften and oil separates.
8. Stir in the blended spinach paste, potatoes, carrots, green beans, cauliflower, green peas, green bell pepper, and soy chunks. Cook covered for 8-10 minutes until the vegetables are half-cooked.
9. Assemble the biryani: Level the vegetable and soy gravy at the base of the pot. Layer the partially cooked basmati rice evenly over the top.
10. Drizzle the saffron-infused milk and remaining ghee over the rice. Scatter the fried onions (birista), chopped coriander, and torn mint leaves on top.
11. Seal the pot with a tight-fitting lid or foil. Cook on low heat (dum) for 15-20 minutes until the rice is fully cooked and aromatic.
12. Gently fluff the biryani layers with a fork from the sides and serve hot with raita and salad.