This looks extremely yummy.
I can give you some additional tips on this
When you marinate the mutton, you can add a little of ginger garlic paste (very fine paste), in the marination you can also use fenugreek seeds grinded fine powder. You do not need to use the chopped ginger and garlic later in the sauteing part.
The onion and tomatoes after sauteing it, let it cool and make a very fine paste, and then cook it again.
It will give a very smooth texture to the curry.

And the nans, I have never tried my hands on them till date. Your's look super tasty