Preparation 

1. Smoke the mustard oil if using.
2. Chop the onion finely.
3. Mince the ginger and garlic.
4. Puree the tomatoes.
5. Crush the coriander and fennel seeds coarsely in a mortar and pestle or a spice grinder.

Instant Pot Method

1. Turn on your instant pot to saute (normal), add the oil and let it heat up. Add the fenugreek seeds and when they turn dark brown (a few seconds), add the rest of the whole spices. Let them sizzle in the hot oil for 10 seconds.
2. Add the chopped onions and fry until they turn golden brown (5 minutes).
3. Tip in the ginger garlic paste, Kashmiri red chilli and turmeric powders. Saute for about 3 minutes adding splashes of water to prevent the masala from sticking to the pot.
4. Add the tomato puree, salt and chicken and cook until the masala is well roasted and the oil separates (10 minutes). Achari masala is done.
5. Cancel the saute mode and switch on the pressure cooking (manual in some models) mode. Secure the lid, seal the vent and set the timer to 4 minutes.
6. Once the timer beeps, release the pressure after 5 minutes. Chicken achari curry is ready. Garnish with chopped cilantro and serve hot with naan and onion rings.

Stove-top Method

1. Cook the chicken in a heavy bottomed deep pot like a wok or karahi , not a shallow pan.
2. Follow the steps until step 4, then cover the pot, lower the heat and simmer for half an hour to 45 minutes. If you find the gravy is getting dry, add a few splashes of water to keep it moist. The final dish has a thick, not thin gravy, but you still need a little water to cook the chicken.
3. Do keep the heat low after step 4 and cover the pot to seal in the flavor. The chicken will cook in its own juices and you will get a moist and succulent chicken curry in the end.