Place all ingredients in the Instant Pot EXCEPT for the butter, cream and 1 tsp of the garam masala.
Mix the ingredients all in the pot with a spoon, then place the chicken on top. If chicken is frozen, push it into the sauce.Don’t add extra liquid.
Place lid on Instant Pot and pressure cook a thigh setting for 10 minutes, then let the pressure release naturally for another 10 minutes. Then release all pressure.
Carefully open the Instant Pot, take the chicken out and set aside.
Blend the remaining sauce with an immersion blender if possible, or a blender. Let the mixture cool a bit.
At the finish add the butter, cream and garam masala. Reheat and mix well.
The recipe says to remove half of the sauce at this point, but I find it tastes too good and usually end up eating it all in a few sittings.
Add the chicken back in (I usually shred it or cut into smaller pieces - up to you).
Serve over rice or noodles or nothing at all.