Turn your Instant Pot onto Saute mode.
Add the butter. Once it melts, add the onion and cook for 2 minutes, then add the ginger. Cook for 2 minutes more, then add the garlic and cook for another 3 minutes until the onion becomes translucent.
Push the aromatics to the side of the pot and add the tomato paste. Add the 2 tablespoons of chicken stock and cook the tomato pasta for a minute or two. Stir so it doesn't burn or stick to the bottom of the Instant Pot.
Add the chicken thighs to the pot and stir to coat the chicken with the rest of the ingredients.
Add the ¾ cup of chicken stock, put the lid on the Instant Pot making sure the pressure (steam) release valve is in the Sealing position. Depending on your Instant Pot, you may have or may not have a Poultry mode. Mine does not so I just set it for Meat and set the timer for 14 minutes and let it start.
It takes 5 to 10 minutes for the steam to build up and before the timer starts to count down. Once the time is up, do a Quick Release being careful not to burn yourself with the steam.
When the Instant Pot releases all its pressure, remove the lid, add the potatoes and the garam masala, stir and place the lid back on top. Set the control panel to Manual cook for 7 minutes again making sure the pressure release valve is set to the Sealing position.
When time is up, do another quick release. When the pressure is completely released, carefully remove the cover and turn off the Instant Pot.
Add the sour cream and stir to combine with the other ingredients.
Serve over basmati rice. I used my rice maker to make the rice. I could have used the Instant Pot but I wanted them to be done at the same time.