Set the Instant Pot on SAUTE and keep it at NORMAL mode. Add oil, when the oil becomes moderately hot gently add the mutton pieces and fry them stirring continuously.
When the meat changes its color and becomes opaque add the ginger garlic paste and fry well until the raw smell of the ginger and garlic completely disappears. Scrape the bottom of the steel pot occasionally with the spatula while frying the meat.
Next, add all the dry spices and fry well until the spices are well roasted, until the raw smell completely disappears and until oil begins to ooze out. This is very important. If you do not fry well your gravy will lack color and taste flat and bad. At this stage, things will get sticky and so keep on frying with intermittent splashes of water. The short splashes of water will prevent the masalas from getting burnt. Don't worry about the sticking part, it boosts the flavors of the dish. Just keep on scraping the bottom and keep on adding splashes of water.
After frying for quiet sometime you'll notice streaks of oil appearing and you'll notice a lovely, dark and gorgeous colored meat well coated with buna masala (roasted spices). This is exactly what we want. Refer the VIDEO.
Press the CANCEL button and turn off the Instant Pot. Allow the steel pot to cool down a bit , say approximately 5 mins. Than, add the beaten curd and mix well with the Bhuna mutton. the yogurt won't curdle and you'll have a fantastic smooth silky textured gravy.
After mixing the yogurt well with the bhuna mutton turn back the SAUTE mode and fry for sometime unitl the yogurt is well roasted and you begin to see streaks of oil appearing.
Now, add the Birista paste and keep on frying until you see streaks of oil appearing. It won't take much time as birista is already fried onions made into a paste. You may add splashes of water if things get sticky.
Add water and de-glaze the steel pot of the Instant Pot very well with the help of your spatula. You need to scrape off slightest of bits and crumbs that's stuck at the bottom of the pot.
Once, de-glazing is over CANCEL the SAUTE mode and close the lid of the Instant Pot. Seal the Valve and press the PRESSURE COOK button and set it on HIGH for 14 minutes.
Once, the cooking cycle is over the Instant Pot will begin to beep. Do a quick pressure release and open the lid.
Add the potatoes + green chilies and close the lid again and seal the Valve. PRESSURE COOK on HIGH for 10 mins.
Once the cooking cycle is over the Instant Pot will begin to beep. Wait for natural pressure release (NPR) for 5 mins and than release the rest of the pressure manually.
Open the lid and serve the Aloo Gosht hot. Enjoy!