Remove the pork from its package and place on a cutting board. If necessary, cut the pork in half so that it will fit in the instant pot.
In a small bowl, mix together the seasonings and rub evenly over all sides of the pork.
Turn the Instant Pot on to saute mode. Once hot, add the olive oil. Add the pork tenderloin and sear for 2-3 minutes per side, then remove the roast to a plate.
Pour ¼ cup of the broth into the pot and use a wooden spoon to (deglazscrape up any browned bites on the bottom of the pot.
Turn the pot off, and pour in the remaining broth. Add in the the sliced potatoes, and set the pork on top.
Place the lid on the pot and set the valve to seal. Set the pot to manual or meat setting for 5 minutes.
Once the 5 minutes is up, do a natural pressure release (allow the pot to come back to pressure on its own, do not open the valve).
When the pressure has released naturally, open the valve, then open the lid of the instant pot.
Transfer the roast to a large serving platter and cover loosely with foil.
FOR THE POTATOES:
Use a slotted spoon to remove the potatoes to a large bowl.
Add the milk, butter, sour cream, and seasonings to taste.
Mash to desired consistency with a potato masher or hand mixer.
FOR THE GRAVY:
Turn the Instant Pot on to saute (higmode.
Once the liquid is boiling, use a small bowl to stir together the cornstarch and water until smooth.
Whisk the cornstarch mixture into the broth, whisking constantly for 1-2 minutes until thickened.
**NOTE: For the potatoes, make sure to slice each one into 3-4 thick slices, if they are any smaller, they will dissolve in the liquid.NOTE: This recipe does not work well with frozen tenderloin. Please use fresh, or thaw your pork first.