In a heavy bottom pan or pressure cooker heat oil and add garlic, black seed, curry leaves, mustard and cumin seed. Fry for 1 minute.
Add in the chopped onions and cook until it becomes translucent or pink.
Add Ginger garlic paste and Mutton. Cook for 3 minutes on high flame.
Now add the prepared Achari spice mix salt, ,red chilly, turmeric and garam masala powder. Cook on medium flame for 4-5 minutes until the meat is coated well with the masala.
Mean while in a pan boil water & add 3 medium tomatoes. Let it boil for 4-5 minutes. Remove the skin and grind the tomatoes to make puree.
Now add prepared tomato puree and cook for 2 minutes.
Add yoghurt and cook on high fallen for 3-4 minute. It may take some time to cook after adding few ingredients but do not skip any step.
Add 1cup of water if you're cooking in a pressure cooker ,But if you're cooking in a pot or pan add 2 or more cups of water or as needed to cook the mutton .
Cook until the meat is tender and cooked completely.
Add in the lemon juice, chopped coriander and green chillies.Check for salt and add if needed. Serve Hot with naan or rice. Enjoy.