How to Make It
Place potatoes, onion, celery, oil, and garlic inside an Instant Pot; select “Sauté” setting. Cook, stirring often, until onions have slightly softened, 6 to 8 minutes. Add ham hocks and stock. Close and lock Instant Pot lid; position the steam release handle to “Sealing” position. Set to “High Pressure” for 20 minutes.
Carefully open the pressure release, and let steam fully escape. Unlock Instant Pot lid. Remove ham hocks; transfer to a work surface to cool slightly, about 10 minutes. Meanwhile, mash mixture in Instant Pot to desired consistency using a potato masher (leaving more whole pieces for a chunkier soup, or mashing more for a smoother soup).
Remove and discard fat and skin from cooled ham hocks. Remove meat from hocks, and chop coarsely. Discard ham bone. Stir heavy cream, salt, pepper, and ham meat into soup. To serve, ladle soup evenly into 8 bowls. Top bowls evenly with cheese, sour cream, and scallions.