Sauté onions and mushrooms in 1 tablespoon oil until tender, about 5 minutes. Let cool
In a large bowl, combine all meatball ingredients, including cooled onions and mushrooms. With your hands, combine well.
Form into 20-24 meatballs and arrange on a sheet pan. At this point, meatballs can be frozen for later use if desired.
Heat remaining oil in a large saute pan over medium heat. Add meatballs, one by one, keeping them from touching and brown. Continue until all meatballs have been browned and remove from pan.
Drain all but about 1 Tablespoon of grease from pan. Add 2/3 cup Portobello Mushroom Sauce and ½ cup chicken stock and return to heat. Return meatballs to pan, bring to boil and reduce to simmer.
In a small dish, combine flour and water well to create a slurry. Slowly add the slurry to the meatballs and sauce stirring gently to combine. Cover and return to simmer until meatballs are done, about 15 minutes.
Remove cover and slowly add ½ and ½, stirring until combined. Add parsley and pepper and serve over egg noodles.