Savory cooked spinach in a creamy Parmesan white sauce, topped with more nutty salty Parmesan and baked to comforting side dish perfection. This Cheesy Creamed Spinach Gratin Casserole is perfect for holiday meals, or even for a nice Sunday family dinner. Want to change how much you make? Use the servings slider on the recipe card to easily adjust the amount.
Spray a 1 ½ quart shallow baking dish with non stick cooking spray.
Fill a large pot about halfway with lightly salted water, and bring to a boil over high heat. Add the cleaned spinach to the boiling water in large handfuls, adding more spinach as it wilts. When all the spinach is in the pot, cook (blanch) for 1 minute. Drain the cooked spinach in a colander while running cold water over it to cool it. Once it has cooled, drain all the water out, and squeeze the spinach with your hands to remove as much liquid as possible. Coarsely chop the drained spinach.
Heat the milk in a small saucepan until hot. Place the oil in a medium saucepan, and heat over medium heat. Once the oil is hot, add the onion, and cook until translucent and softened but not colored, about 5 minutes.
Stir in the flour, salt, pepper, and cayenne and cook, stirring constantly, for 2 minutes. Slowly stir in the milk, raise the heat to medium-high, and cook, stirring frequently, until the sauce bubbles and thickens, about 5 minutes.
Add 1 cup of the Parmesan cheese to the sauce, and stir until the cheese is melted and thoroughly combined.
Remove the pan from the heat, and stir in the chopped spinach, mixing well. Taste for salt and pepper, adding more if necessary. Pour the spinach mixture into the prepared baking dish, sprinkle the remaining ¼ cup Parmesan on top, and bake until the gratin nicely browned, about 35 minutes. Let cool a few minutes before serving.