Start by laying the quartered potatoes in the bottom of your pressure cooker in an even layer. Pour the chicken broth over the top. Lay the rack that comes with your pressure cooker over the top so it lays flat.
Combine the ingredients for the meatloaf (minus the topping) in a large bowl until fully combined. Shape the meat mixture into a loaf and place on a piece of tinfoil. Shape the tinfoil up and around the edges of the meatloaf, creating a pocket for it. Place the meatloaf on top of the rack in the pressure cooker and secure lid.
Ensure that the steam release is closed and turn pressure cooker to Manual mode for 20 to 25 minutes*. Once finished cooking, use the quick release method to let the steam escape. Check meatloaf for internal temperature of 155 degrees F.
Carefully lift the meatloaf out of the pressure cooker and place on a baking sheet. Mix the ingredients for the topping and brush all over the meatloaf. Place meatloaf under the broiler for just 3 to 4 minutes, until the top is bubbly and caramelized.
Meanwhile add the remaining ingredients (half and half, butter, sour cream, garlic powder, salt and pepper) to the instant pot and mash the potatoes until smooth and creamy.
Serve the meatloaf in slices with the mashed potatoes. Enjoy!
UPDATE Some people are finding that 20 minutes is not enough time to fully cook their meatloaf. I use an 8 quart Instant Pot for this recipe and 20 minutes works great. If your meatloaf still hasn't reached 155 degrees F in the pressure cooker, cover and cook an additional 5 minutes at high pressure. Once it's cooked through finish with the topping and broil.