Heat the bacon fat in the Instant Pot on the highest saute setting. Add the cabbage and saute for 2-4 minutes, until softened.
Add the tomato paste and stir. Add the potatoes, carrots, corned beef and seasonings and stir to combine.
Add the stock and cream (optional) and set the Instant Pot to pressure cook on high for 15 minutes.
Use the quick release to release the pressure when done cooking. Season with additional salt as necessary and serve with crusty bread.