In a bowl, mix all marinade ingredients: yogurt, ginger-garlic paste, chopped coriander stems, chilli flakes, cumin powder, coriander powder, garam masala, black pepper, salt, vinegar, and oil.
Add chicken pieces to the marinade, coat well, and marinate for 30 minutes to 1 hour.
Heat oil in a wide pan over medium heat. Add marinated chicken, cover, and cook, turning occasionally, until well browned and fully cooked (the marinade will reduce and form thick pan drippings). Alternatively, air fry at 180°C for 18–22 minutes flipping halfway, or bake at 200°C for 35–40 minutes turning once.
Remove cooked chicken from pan and set aside.
In the same pan, melt butter. Add chopped onion and green chillies; sauté until soft and lightly golden.
Add atta (or maida) and cook for 1 minute, stirring.
Slowly whisk in cold milk until smooth.
Add cheese slice, chilli flakes, black pepper, and salt; cook until sauce lightly thickens.
Return chicken to the pan, coat with sauce, and simmer for 2 minutes.
Finish with chopped coriander leaves and serve hot with roti, rice, or salad.