Make a fine paste of chopped garlic, ginger, and green chilies. Marinate mutton pieces with this paste, yogurt, and salt for 30 minutes.
Wash the spinach leaves and cook in boiling water with some sugar for 3 minutes. Remove the leaves from hot water and place them in ice water for some time. Grind the leaves to a coarse paste and set them aside.
Heat cooking oil in a pressure cooker and add all the whole spices. Add chopped onion and fry till light golden in color.
Now add the marinated mutton, 1 tablespoon coriander powder, 2 teaspoon cumin powder, chopped tomato, and 3 cups of water (or as needed) in which spinach was cooked. Place the lid and cook the mutton for 15 minutes on medium heat. Once the pressure drops, open the lid and check if the mutton is cooked. Add salt if needed.
Finally, add spinach puree, garam masala powder, lemon juice, and coriander leaves. Taste and check the seasoning. Cook the curry on low flame for 5 minutes.
Turn off the flame and serve hot.