In a large bowl, combine the ground turkey, egg milk onion powder, parsley, thyme salt and pepper until just combined. Shape Into 20 (1-Inch or 2.5 cm) meatballs.
Press Saute on your electric pressure cooker. When the inner pot Is hot add the oll and brown the meatballs, 2 to 3 minutes per side. Once the meatballs are brown transfer them to a serving dish and set aside.
Add the sliced onlon to the pot and cook until just tender 3 to 4 minutes. Add the garlic and cook for an additional 30 seconds. until fragrant. Add 1 cup (235 ml) of the beef stock to the pan and scrape up any browned bits on the bottom of the pot.
In a small bowl, combine the remaining 1/2 cups (353 ml) beef stock, sour cream, potato starch, paprika, tomato paste bouillon. and Worcestershire sauce. Stir until well combined. Add to the onion mixture already in the pan. Return the meatballs to the pot submerging them completely in the sauce.
Close and lock the lid making sure the steam release handle is In the sealing position. Cook on high pressure for 10 minutes. When the cooking time is finished turn off your pressure cooker and allow a natural release of 20 minutes or until the float pin drops. When the float pin has dropped unlock the lid and open It carefully.
Add the sliced mushrooms to the pot. Stir well, then close the lid and let sit for 3 minutes to soften the mushrooms.
In a small bowl mix the cornstarch and cold water together to create a slurry. Press Sauté or Browning on your electric pressure cooker again and allow the sauce to heat up. When the sauce Is bubbling add the cornstarch mixture to the pot and whisk constantly for 2 minutes or until the sauce thickens. 8. Sprinkle with additional parsley, if desired.