In the same pan heat one tablespoon butter. Add the onion and fry until golden brown. Add the ginger/garlic paste and fry for a minute
Add the turmeric, chilli powder, cumin and coriander. Fry for a minute
Add the passata and water. Season with salt
Cook for 20 minutes or until it's slightly thick and the oil surfaces to the top
Place in a glass jar/bowl and blend into a smooth paste
Return to the pan. Add the cream and sugar and heat through
Add the meatballs into the sauce. Add the dried methi leaves, rub them between your fingers and sprinkle into the curry
Simmer for 5 minutes until the meatballs are cooked. Sprinkle in the garam masala
Garnish with coriander and serve hot with naan bread