Step 1: Boil and Shred the Chicken — Bring 4 cups of water to a boil in a large pot. Add the salt, turmeric, bay leaf, and the chicken thighs. Lower the heat to a gentle simmer and cook for 18–20 minutes until the chicken is cooked through (165°F / 74°C internal temperature). Lift the chicken out with a slotted spoon and reserve the cooking liquid — it's liquid gold for the gravy. Let the chicken cool for 5 minutes, then shred it finely using two forks, pulling along the grain into thin strands.
Step 2: Make the Cashew Paste — Drain the soaked cashews and blend with 2–3 tablespoons of fresh water into a completely smooth paste. Scrape down the blender and blend again — there should be no gritty bits. Set aside.
Step 3: Sauté the Aromatics in Mustard Oil — Heat the mustard oil in a large, heavy pan or kadhai over medium heat until it just begins to smoke lightly, then lower to medium. (Heating mustard oil to smoking point mellows its sharpness.) Add the finely chopped onions and cook for 8–10 minutes, stirring often, until deep golden and caramelized at the edges. Stir in the ginger garlic paste and slit green chilies; cook 1 minute until fragrant.
Step 4: Build the Gravy — Add the chopped tomatoes and cook for 5–6 minutes until they break down into a thick paste. Stir in the cumin powder, coriander powder, Kashmiri red chili powder, turmeric, and salt; cook 1 minute to bloom the spices. Pour in the cashew paste and 1½ cups of the reserved chicken cooking liquid. Bring to a simmer and cook for 8–10 minutes, stirring occasionally, until the gravy thickens and a thin layer of oil glistens at the edges.
Step 5: Add the Shredded Chicken — Fold the shredded chicken into the gravy, making sure every strand is coated. Simmer on low for 5–7 minutes so the chicken absorbs the gravy. Stir in the garam masala, crushed kasuri methi, butter, and fresh cream. Taste and adjust salt and heat — this is when the Kolkata-restaurant aroma really hits.
Step 6: Garnish and Serve — Transfer to a serving bowl. Arrange the halved boiled eggs on top, cut-side up, drizzle with a swirl of cream, and sprinkle with fresh cilantro. Serve hot.