How to Make It
Preheat oven to 425º. Sauté onions in a lightly greased large nonstick skillet over medium heat 6 minutes or until tender. Add flour, and cook, stirring constantly, 30 seconds to 1 minute. Add milk; cook, stirring frequently, 2 to 3 minutes or until thickened. Remove from heat.
Stir in 1/4 cup Parmesan cheese and next 4 ingredients. Add spinach, and stir until thoroughly combined. Transfer spinach mixture to a lightly greased 8-inch square baking dish. Sprinkle with remaining 1/2 cup Parmesan cheese.
Bake at 425º for 15 minutes or until cheese is melted and mixture is bubbly. Let stand 5 minutes before serving.