In a large bowl, combine ground beef, plain bread crumbs, egg, pepper, salt, nutmeg, allspice, and Worcestershire Sauce. Mix to combine ingredients. Do not over mix, this keeps the meatballs tender. Gently roll meat into 2 inch round meatballs, set aside.
Press saute on the Instant Pot add the olive oil to the Instant Pot.
Brown the meatballs on all sides in batches, set aside.
Into the Instant Pot, whisk unsalted butter and flour for about 30 seconds to blend flavors.
Add in 1/3 of the beef broth and use a wooden spoon to scrape up any brown bits at bottom of the pot. Once brown bits are up from the bottom of pot, add the remaining beef broth.
Mix in the Worcestershire Sauce, Dijon mustard, black pepper, and a dash of salt to the pot.
Press cancel. Add the browned meatballs back into the pot. Place the top on the pressure cooker, close the valve. Press pressure cook/high 5 minutes.
When cook time is complete, quick release. Once complete, remove the top of Instant Pot.
Add in heavy cream, press saute for 3 to 4 minutes to thicken the sauce.
Taste for seasoning, reseason if needed. Top with fresh parsley. Serve as an appetizer. For a meal Serve over egg noodles, zoodles, mashed cauliflower.