Sauté onion in butter until tender. In large bowl, beat eggs. Stir in onion, spinach, stuffing mix, and ½ cup cheese. Form into 1-inch balls. Roll in remaining cheese. * Place on greased baking sheet. Bake in preheated 350°F oven until golden brown, 12 to 15 minutes. Heat tomato sauce to serving temperature and serve with tidbits.
* May be frozen after this step. Do not thaw. Bake on greased baking sheet in 350°F oven until golden brown, about 25 minutes.