Combine potatoes, garlic, and broth in Instant Pot. Season with salt and pepper and stir. Lock lid into place and set pressure valve to “Sealing.” Select “Manual” or “Pressure Cook” on High for 8 minutes.
When timer goes off, allow natural release for 10 minutes, then quick release any remaining pressure.
Carefully remove lid. Add heavy cream and butter. Mash with potato masher or immersion blender to desired consistency – smooth or slightly chunky. Taste and adjust seasoning.
Transfer to serving bowl and serve immediately.