Place a dry skillet over medium heat. Add the fennel seeds, cumin seeds, mustard seeds, fenugreek seeds, and nigella seeds. Toast for 1 to 2 minutes until fragrant, stirring constantly to prevent burning. Transfer to a mortar and pestle and crush coarsely. Set aside.

Heat the cooking oil in the same skillet over medium heat. Add the chopped onions and cook until light golden brown, about 6 to 8 minutes. Stir in the ginger paste and garlic paste, cooking for 1 minute until the raw aroma fades.

Add the chopped tomatoes, Kashmiri red chili powder, turmeric powder, and salt. Cook for 5 to 7 minutes until the tomatoes soften and oil begins to separate at the edges. Stir in half of the crushed pickling spice blend.

Add the chicken pieces to the skillet, turning them to coat evenly in the masala. Cook for 5 minutes until the chicken changes color on the outside.

Lower the heat. Whisk the plain yogurt smooth and pour it into the pan while stirring continuously. Add the water and the remaining crushed pickling spices. Bring to a gentle simmer, cover the pan, and cook for 15 to 20 minutes, stirring occasionally, until the chicken is tender and reaches an internal temperature of 74°C / 165°F at the thickest piece.

Uncover the pan, let the gravy thicken slightly for 2 minutes, then garnish with chopped coriander leaves. Serve hot.