Place tomatoes (including juice) in the inner pot. Add garlic, ginger, turmeric, cayenne pepper, paprika, 1 teaspoon garam masala, cumin and salt. Stir/whisk until combined.

Pat chicken dry with paper towels, then lay them on top of the sauce. Do not mix them into the sauce!

Lock lid on Instant Pot. Turn pressure release knob to "SEALING" position. Select "MANUAL"; or adjust to HIGH pressure. Set timer for 10 minutes. It takes 10-15 minutes to reach full pressure, then the 10 minute cooking time will start. Once finished cooking, let pressure release NATURALLY. Do nothing during this time (about 15 minutes). When all pressure is released, pressure button will drop, indicating it's safe to remove lid.

Open lid. Transfer chicken out of the pot (use slotted spoon or spatula) and put it on a cutting board. Let cool a few minutes, then cut each piece into large chunks, about 1½" wide. Set aside.

Make Butter Sauce: Use immersion blender to puree sauce remaining in the inner pot (insert immersion blender directly in the pot to do this). Let sauce cool 2-3 minutes. NOTE: No immersion blender? Carefully transfer sauce in batches to a blender; process until smooth. Once pureed, pour sauce back into the inner pot.

Add butter (in chunks), coconut milk, remaining teaspoon of garam masala and cilantro to the sauce. TIP: Stir coconut milk while still in the can, to combine liquid and solids before adding it! Stir well, until ingredients are fully combined.

NOTE: At this point, remove about ½ of the sauce (or a little less) and save it for another batch. That's right... you won't use ALL the sauce! After it has cooled, freeze the removed sauce in an airtight container OR store it in the refrigerator for 3-4 days and use it again, if desired.

Place chicken back into the sauce remaining in the inner pot; stir until coated.  Press "CANCEL", then select "SAUTÉ"; set pressure setting to "LESS" (low heat). Stir/cook butter chicken (uncovered) until heated through. Serve with rice. Enjoy!