- 5 (10 ounce) packages frozen chopped spinach
- 1/2 cup butter
- 1 onion, chopped
- 2 cups milk
- 2 cups grated Cheddar cheese
- 1/4 cup all-purpose flour
- 1/4 teaspoon ground black pepper
- 3 eggs, beaten
- Preheat oven to 350 degrees F (175 degrees C). Grease one 9×13-inch baking dish.
- Bring a large pot of water to a boil and add spinach. Cover, reduce heat, and cook until heated through, 5 to 6 minutes. Drain well, squeezing out excess moisture with your hands. Set aside to cool.
- Melt butter in a saucepan over medium heat; stir in onion and cook until soft and translucent, 5 to 10 minutes.
- Transfer onions to a double boiler; mix in milk, Cheddar cheese, flour, and ground black pepper; cook and stir until blended and smooth, about 5 minutes. Remove from heat; fold in eggs and spinach. Pour the spinach mixture into baking dish and smooth top.
- Bake, uncovered, in the preheated oven until a toothpick inserted in the center comes out clean, about 30 minutes. Cool briefly before cutting into squares.