Combine ground beef with chopped onion, egg, bread crumbs, salt and pepper. Sh ape mixture into about 24 meatballs, then brown in margarine; drain well.
Stir together tomatoes, water, beef base and seasonings. Palce carrots, potato es and sliced onion in bottom of Crock-Pot; top with meatballs. Pour tomato mi xture over all. cover and cook on Low for 8 to 10 hours.
Before serving, remove meatballs with a slotted spoon. Make a smooth paste of the cornstarch and water and stir into vegetables. Cover and cook on High for 10 minutes ot thicken. Reutrn meatballs to stew and serve.
Serves 6