Combine all the ingredients for the meatballs in a large mixing bowl and knead well with clean hands, until fully combined. Do not overmix or your meatballs will be on the tough side.
Form into approximately 48 small meatballs, roughly the size of a ping-pong ball and place them on the prepared pan. A small spring-loaded cookie scoop really helps to do this task quickly and efficiently.
Bake the meatballs at 450°F for 10 minutes and then decrease the oven temperature to 350°F and continue cooking the meatballs for another 8 minutes, or until they start to turn golden brown.
While the meatballs are baking, cook the mushrooms in a saute pan with fitting lid set over high heat until they're brown and softened, about 8 to 10 minutes.
Add the onions and cook until softened and slightly golden, about 5 minutes.
While the onions and mushrooms are cooking, combine all the ingredients for the sauce in a glass measuring cup; add that to the pan as soon as the mushrooms and onions are cooked to your liking.
Add the par-baked meatballs to the simmering sauce, put the lid on and simmer over medium heat for 5 to 6 minutes. Dilute the corn (or tapioca) starch in the cream (or milk) and add that to the simmering liquid. Delicately mix it in, bring back to a a simmer and allow the meatballs to cook for one full minute, to ensure that the starch has reached its full thickening power and has also cooked completely.
Remove from heat, stir in chopped parsley and serve without delay.