Cook onions according to package directions; drain well and set aside.
In a saucepan, saute garlic in 2 tablespoons butter for 1-2 minutes. Add spinach; cook and stir until spinach is wilted and liquid has evaporated, about 3 minutes. Stir in 1/2 cup Parmesan cheese and cream. Stir in the salt, pepper and reserved onions.
Transfer to a greased shallow 2-qt. baking dish. Combine bread crumbs and remaining cheese; sprinkle over onion mixture. Dot with remaining butter. Bake, uncovered, at 400° for 20 minutes or until golden brown. Serve with a slotted spoon.
Editor's Note: A 10-ounce package of frozen spinach, thawed and squeezed dry, may be substituted for the fresh spinach.