Prepare the spice mix first. Place a pan on medium high heat and sauté the whole spices for about 20 seconds. Let it cool down for a while before grinding it into fine powder. Keep it aside to be used later.
Place a heavy bottom pan on medium heat and pour the mustard oil. Once the oil heats up, drop ¾th of the sliced onion (save the rest for garnish). Sprinkle ½ teaspoon of salt and stir. Cook the onion for 2 minutes and then, add the grated ginger garlic (not the julienned ginger) and sauté for another 3 minutes.
Scatter the mutton cubes, sprinkle 3 tablespoons of the ground spice (prepared earlier) and toss it around to mix everything. Sprinkle the turmeric, ½ teaspoon of salt and sugar. Toss around and mix everything.
Cook the meat in medium heat for about 10 minutes. The spices should be cooked through by then, and you should see oil separating. Pour 4 cups of water and ½ teaspoon salt. Stir around and bring the water to a boil at high heat. Then, reduce the heat to medium, cover the pan and let it simmer for 1 and ½ hours.
While the mutton simmers and gets tender, prepare the fried onion. Place a pan with enough oil to deep fry the sliced onion. It will take about 10 minutes for the onion to turn golden brown. Make sure you pay close attention to the onion and keep stirring occasionally as it get can turn from brown to black pretty fast. Once done, take it off using a slotted spoon into a plate layered with kitchen towel. Keep it aside to be used later for garnish.
To the same oil, drop the julienned ginger for a few seconds and take it off into a separate plate layered with kitchen towel.
After 1 and ½ hours, the meat should be cooked through and tender. If not, continue cooking the meat. Once the meat is cooked through, switch off the heat, uncover the pan and let it cool down completely. Do not stir as the stew cools down because this process will create a layer of oil on top. It should take about 10 minutes to cool down completely.
Once you see the red hue layer on top, take a spoon and carefully scoop it out into a different bowl. Then, turn on the heat and bring the meat to simmer again.
In a bowl, prepare the roux by mixing the flour with water until there are no lumps. Pour this mixture in the stew, little by little, and keep stirring as you do so. Mix around the roux and let the stew simmer for another 10 minutes. This process will thicken the gravy.
At this stage, check for salt and add any, if needed. Finally, add half the chopped green chili and cook for 2 minutes.
For serving, ladle the stew into your serving bowl, drizzle the fat that was kept aside, followed by fried onion, julienned ginger, green chili and some finely chopped cilantro.
Serve it warm with your choice of rice or bread.