Turn your pressure cooker on to the saute mode. Add olive oil, and onions saute until the onions start to get translucent, about 3-4 minutes. Add garlic and stir until fragrant, about 30 seconds.
Place butter over the chicken. Secure the lid on the pressure cooker and make sure that it is sealed. Close the pressure release valve. Set the pressure cooker to manual, high pressure for 10 minutes.
When the cooking is done, allow to naturally release for 5 minutes before opening the lid. Remove chicken. If you would like to thicken the sauce, place the pressure cooker on the saute mode and bring to a boil until thickened.