Heat ghee in a pressure cooker and sauté the onions till light brown. Then add ginger and garlic and sauté again.
Next, add cumin, dry red chilli, cinnamon, garam masala, fennel and salt to taste. Saute for another minute and then add the tomatoes. Cook till the tomatoes are completely broken down and turns mushy.
Add the mutton pieces, season with salt and mix well. Add a dash of vinegar and enough water for gravy. Pressure cook till the mutton is 3/4 ths done; open and add the potatoes. Cook further on medium heat till done. This will also help the gravy to thicken.
Squeeze some lemon juice and garnish with coriander leaves.