Roll the beef mince into evenly sized meatballs.
Heat a tablespoon of oil in a frying pan and brown the meatballs until golden on the outside. They don't need to be cooked through. Transfer them to the slow cooker.
Use about ½ cup of the stock or water to deglaze the pan, scraping up any browned bits, and pour this over the meatballs.
Add all remaining ingredients except the sour cream, cream, spinach if using and corn flour slurry to the slow cooker.Cook on LOW for 5–6 hours or HIGH for 2–3 hours, until the meatballs are cooked through.
Prepare the mashed potatoes ready for serving.
Stir the sour cream and cream into the slow cooker.
Mix corn flour with a little cold water and add gradually to thicken the sauce to your liking.
Spoon the Beef Meatball Stroganoff over mashed potatoes and garnish with fresh parsley before serving.