Select "Saute" on the Instant Pot. Allow pot to heat, it will indicate "Hot" on the display when ready.
Add 2 tablespoons of butter to the pot and allow 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 the lid.
Press "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 up and build up the 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.
Carefully remove the lid, opening the top away from you as steam will be released from the pot.
Remove the chicken from the pot 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 butter chicken.
Taste the sauce and add more salt as needed.
Garnish butter chicken with chopped cilantro.
Serve butter chicken with basmati rice or naan bread.