Combine chicken pieces with yogurt, ginger-garlic paste, lemon juice, chili powder, turmeric, garam masala, and salt in a bowl.

Mix well to coat the chicken thoroughly, then cover and refrigerate for at least 30 minutes, or preferably for a few hours.

Heat vegetable oil in a large pan over medium-high heat.

Add the marinated chicken pieces and cook until browned on all sides and cooked through, about 7-10 minutes.

Remove the chicken from the pan and set aside.

In the same pan, melt the butter over medium heat.

Add chopped onions and sauté until softened and translucent, about 5-7 minutes.

Stir in cumin powder, coriander powder, and green chili (if using), and cook for 1 minute until fragrant.

Pour in the tomato passata, bring to a simmer, then reduce heat and cook for 10-15 minutes, stirring occasionally, until the sauce thickens.

Stir in the heavy cream and crushed fenugreek leaves, then return the cooked chicken to the pan and mix well.

Simmer for another 5 minutes to allow the flavors to meld, then taste and adjust seasoning if necessary.