Add all of the meatloaf ingredients to a large bowl and gently mix everything to combine (without over-working the meat).

Form the meat mixture into a round loaf that will fit into your instant pot.

Place the loaf on a large piece of aluminum foil and fold the edges up to make a secure nest for the meatloaf to rest in. (You want the edges high enough that grease from the loaf wont spill out onto the potatoes while cooking.)

Add the quartered potatoes, water, and salt to the bottom of the instant pot.

Lay the IP wire rack on top of the potatoes. Place the aluminum foil "nest" with the meatloaf on top of the rack.

Secure the lid on the pot and close the pressure release valve. Select manual/High pressure and cook at high pressure for 25 minutes*. When the timer beeps, allow the pressure to naturally release for 10 minutes.

While the meatloaf cooks, make the sauce by combining all of the sauce ingredients in a bowl.

Remove the IP lid, and carefully remove the meatloaf. Discard the aluminum foil and drippings. Spoon the meatloaf sauce over the top and cut into slices.

Drain any remaining water from the pot. Add the milk, sour cream, butter, bouillon paste, and salt and pepper to the bottom of the instant pot with the mashed potatoes. Mash to combine (but don't over-mash the potatoes). Taste and adjust seasonings, as needed.