Clean the Mushrooms: Rub mushrooms with a little flour to remove grit, rinse quickly, and pat dry. Halve large mushrooms and keep small ones whole.
Temper Whole Spices: Heat mustard oil in a heavy pot until it smokes lightly. Reduce heat to low and add bay leaves, cinnamon, cardamom, and cumin seeds until fragrant.
Caramelize the Base: Add sliced onions. Sauté on medium heat, adding splashes of hot water occasionally to help them turn deep golden and jammy without burning.
Add Aromatics: Stir in the ginger-garlic-chili paste and sauté for 4 minutes until the raw aroma disappears.
Build the Gravy: Lower heat. Add turmeric, chili powder, and coriander powder. Add the sliced tomatoes, whisked yogurt, and salt. Sauté until the oil separates from the masala.
Simmer: Add 1 cup of hot water. Cover and simmer on low for 10 minutes until the gravy is thick and glossy.
Cook Mushrooms: Fold in the mushrooms. Cover and cook for 5–7 minutes. They will release moisture and soak up the spices.
The "Do Pyaza" Tempering: In a separate small skillet, heat 1 tsp oil on high. Flash-sear the onion petals, slit green chilies, cilantro stems, and crushed coriander seeds for 60 seconds.
Combine & Finish: Pour the hot onion-petal mixture over the mushroom curry. Sprinkle with roasted fenugreek leaves, garam masala, ginger juliennes, and fresh cilantro.
Serve: Mix gently and serve hot with buttery flatbreads or steamed Basmati rice.