Blend the Base: Place tomatoes, garlic, ginger, cilantro stems, green chili, and soaked cashews in a high-speed blender. Process until it forms an absolutely smooth, grit-free puree.
The Flour-Clean Method: Toss the mushrooms with 1 tablespoon of flour to lift dirt. Rinse quickly under cold water, pat dry immediately, and cut into chunky halves or quarters.
Sauté Aromatics: Heat oil and 2 tbsp butter in a heavy pan. Sauté whole spices for 30 seconds. Add minced onions and cook until light golden brown.
Bloom the Spices: Turn heat to low. Add chili powder, turmeric, and coriander powder with a splash of hot water. Sauté for 1 minute until fragrant.
Simmer the Gravy: Pour in the master puree, salt, and sugar. Cover and cook on low-medium heat until the oil begins to separate and rise to the surface.
Cook Mushrooms: Add the mushrooms to the gravy. Sauté on high for 2 minutes, then add 1/2 cup hot water. Cover and simmer for 5 minutes.
The Glossy Finish: Turn off the heat. Stir in the heavy cream, a small knob of extra butter, crushed fenugreek leaves, and garam masala.
Garnish: Top with fresh cilantro and serve with warm Naan or Garlic Roti.