Heat oil in a pot and fry onions until golden.
Add whole spices and fry until spices crackles.
Mix in grounded spices, stir for few seconds, then mix in mutton pieces. Cook on medium heat for another 5 minutes until the meat has changed its color.
Next, pour 2 cups of water in the pot. Close the pot with a tight lid and cook on medium heat for 45 minutes until meat is very soft and coming off the bones. ( You can pressure cook too.)
Dry roast wheat flour on medium heat with constant stirring. Remove flour from heat. Mix wheat flour with 1 cup of water to form a slurry without any lumps. Set aside.
When the meat is cooked add wheat flour slurry and yogurt to it. Mix well and add 1 cup of water (less or more as needed for desired consistency). Cook for another 5-7 minutes until oil separates.
Add butter in the last and simmer for 1 minute. Garnish with ginger and serve with hot naan and lemon wedges.