Select "Saute" on the Instant Pot. Allow pot to heat, it will indicate "Hot" on the display when ready.
Add 2 tablespoons of butter and allow it to melt.
Add in the onions, ginger, and garlic, saute and occasionally stir until onions are tender, about 5 minutes.
Make a well in the center of the pot. Add in 1 tablespoon of butter, garam masala, coriander, paprika, turmeric, and salt.
Stir spices with butter and vegetables, cook until fragrant, 1 minute.
Add in crushed tomatoes, stir to combine.
Submerge chicken breast in the sauce.
Make sure that the release valve is in the "Sealing" position. Place the lid on the Instant Pot, turn and lock.
Press the "Manual" button on the Instant Pot on high pressure, and then set the timer to 10 minutes using the "+" or "-" buttons. It will take about 10 minutes for the pot to heat and build up pressure. You will see some steam release from the lid, and then the time will start on the display.
Once cook time is complete, allow pressure to naturally release for 10 minutes.
Use an oven mitt or towel to slowly and carefully twist the steam release handle on the lid to "Venting" position. The initial release will spray some moisture around the pot so be careful.
Remove the lid, opening the top away from you as steam will be released from the pot.
Remove the chicken and transfer to a cutting board.
Chop the chicken into chunks, about 1-inch in size.
Add 1 tablespoon of butter and coconut milk to the sauce, stir to combine.
Use a hand-held immersion blender or transfer to a blender to process the sauce into a smooth puree.
Add chopped chicken and peas to the sauce, stir to combine until warmed through.
If needed, turn the Instant Pot to "saute" to reheat the chicken.
Taste the sauce and add more salt as needed.
Garnish with chopped cilantro.
Serve butter chicken with basmati rice or naan bread.
Heavy cream can be substituted for coconut milk for a richer sauce.
MAKE IT WHOLE30 AND PALEO: Substitute ghee or coconut oil for butter, and sea salt for kosher salt.
MAKE IT DAIRY-FREE: Use coconut milk and coconut oil instead of heavy cream or butter.
MAKE IT KETO: Use heavy cream instead of the coconut milk and omit the peas.