Place all of the ingredients except for butter and garnishes in an Instant Pot and give it a good stir.
Move the vent to “seal”. Press MANUAL and cook on HIGH for 45 minutes.
Once the 45 minutes are up, let the pressure release naturally for 25 minutes. Then, move the vent to “venting” and let the remaining steam release.
Open the lid. Ladle 2-3 cups of the cooking liquid into a bowl or measuring cup. Drain the beans into a large colander.
Return the beans to the pot and use an immersion blender (or potato masher) to puree the beans. Add in some of the cooking liquid until your desired consistency is reached. Add butter and stir until melted.