Set Instant Pot to "saute". While heating up, season your pork with about half the seasoning recipe above. Or skip this step if you have a pre-marinated or pre-seasoned pork tenderloin.
Once Instant Pot is hot, add oil and then add seasoned pork. If tenderloin is too long it can be cut in half prior to adding. Brown on all sides, about 3 minutes per side.
Once pork is browned, remove with tongs and set aside on a plate. Pour in ¼ C broth and scrape all the bits up from the bottom of the pot (deglaze). Pour in remaining broth. Place pork back in the pot. Arrange potatoes in steamer basket and place basket on top of the pork.
Press cancel to stop saute mode. Cover, seal vent and set manual high pressure for 8 minutes. (larger cuts will require more time)
When 8 minutes is up, allow a natural release. Using tongs or a safe "mitt", remove potato steamer basket. Place pork on a cutting board and allow to rest.
Once again, press saute. Once broth comes up to a boil, stir 3 T cornstarch together with 3 T cold water or broth and whisk in to pot with broth. Allow to saute, occasionally whisking until thickened. Cancel saute.
While gravy is thickening, prepare potatoes. Place potatoes in a bowl and mash. Add salt, pepper & butter and slowly add in cream/milk until desired consistency. If you prefer you can whip them with a hand mixer instead.
Slice pork and serve with gravy and potatoes on side.