In a large bowl combine mashed potatoes, crumbled cheese, chopped onion, bell pepper, ginger garlic paste, ground coriander, cumin, red chili powder, turmeric powder, milk, coriander leaves, and salt.Mix it with your hands until all ingredients are properly mixed and dough is formed.Divide the dough into equal portions and shape them into small balls.
Heat the oil in the pan and fry the koftas until they are browned from each side.
In a separate pan melt the butter over medium heat and saute onion until translucent.
Add all the ingredients except milk, heavy cream, tomato puree, and garam masala and cook them until they are soft.Now blend these softened ingredients in a blender.
Now in a pan heat some butter add that blended material and cook for one minute.Add tomato puree and cook until it thickens and the raw smell disappears.
Add milk, heavy cream, garam masala and water. Bring to a boil.Reduce heat and let it simmer for 7-8 mins. Adjust salt according to your taste.Transfer the gravy to a bowl, gently put koftas in the gravy, and sprinkle coriander leaves. Enjoy with naan or rice.