Place meat, breadcrumbs, egg & seasonings together in a bowl & mix well. Turn onto a floured board & shape into 16 balls.
Heat oil in frying pan & fry meatballs until brown all over. Lift out onto plate.
Peel & chop onion, peel carrot & cut into slices, slice leek & celery, quarter mushrooms. Add to pan & fry slowly.
Place cornflower & sugar in a bowl & gradually stir in water. Add ketchup, vinegar & soy sauce & pour into frying pan, season and cover with a lid or foil. Cook for 30 minutes. Serve with ribbon noodles or mashed potatoes.