In a large bowl, combine all of the meatloaf ingredients and gently stir together until well combined. (I like to do this by hand, but you can use a spatula or fork too.)

Shape the mixture into an 8x5-inch loaf and place on a piece of foil large enough to extend a couple of inches around each side of the meatloaf. Shape the foil around the meatloaf into a boat by folding up the edges an inch or so. (This will catch any drippings.)

In the Instant Pot, arrange the potatoes in an even layer. Add the water and sprinkle with ¼ teaspoon salt of salt. Place the trivet on top of the potatoes, then set the foil with the meatloaf on top of the trivet.

In a small bowl, stir together the glaze topping ingredients until smooth. Spread a third of the glaze over the meatloaf.

Secure the lid and steam valve. Cook under High pressure for 20 minutes. Naturally release the steam for 10 minutes, then Quick release the remaining steam.

Carefully remove the meatloaf and trivet. Spread the remaining Glaze over the meatloaf. If desired, place the meatloaf on a baking sheet and broil for 3 to 4 minutes or until the glaze is bubbly and caramelized.

Meanwhile, drain the cooking liquid off of the potatoes. Keeping the potatoes in the pot, add the remaining ½ teaspoon salt, sour cream, butter, milk, and pepper. Mash the potatoes to the desired consistency. Slice the meatloaf and serve with the mashed potatoes.