Go Back
+ servings
Easy make ahead Spinach Gratin being served.
Print Recipe
5 from 9 votes

Easy Make-Ahead Spinach Gratin

Easy Make-Ahead Spinach Gratin is full of creamy, cheesy goodness. Frozen spinach is mixed with a classic Mornay sauce accented with caramelized onions. It's topped with both Gruyère cheese and freshly grated Parmesan cheese to create an unforgettable dish. 
Prep Time15 minutes
Cook Time20 minutes
Total Time35 minutes
Course: Side Dish
Cuisine: American
Servings: 6 servings
Calories: 201kcal


  • 24 ounce package frozen chopped spinach, thawed
  • 2 Tablespoons unsalted butter
  • 2 cups finely chopped onion (1 large onion)
  • 2 Tablespoons all-purpose flour
  • 1 teaspoon Kosher salt
  • ¼ teaspoon freshly ground black pepper
  • teaspoon freshly grated nutmeg (See Tip 1)
  • 1 ½ cups milk (See Tip 2)
  • ½ cup (2 ounces) freshly grated Parmesan cheese, divided
  • ½ cup shredded Gruyère cheese


  • Preheat oven to 425°F. Spray a 2-quart casserole dish with non-stick spray. Set aside.
  • By the handful, squeeze as much water as possible from the spinach. Repeat with paper towels. Set aside. 
  • Melt the butter in a large skillet over medium heat. Add the onions and sauté until lightly browned about 15 minutes. Add the flour, salt, pepper, and nutmeg. Cook, stirring, for 2 more minutes. Add the milk and cook until thickened. Add ¼ cup of grated Parmesan cheese. Stir until melted. Add the spinach; mix well.
  • Transfer to the prepared casserole dish. Top with Gruyère cheese and remaining Parmesan cheese. May be prepared in advance up to this point. (See Tip 3)
  • Bake in preheated 425°F oven for 20 minutes or until hot and bubbly.
  • Yield: 6 servings. (See Tip 4)



  1. I like to use fresh nutmeg. However, you can also use ground nutmeg in this dish.
  2. I used whole milk, but feel free to use 2% milk.
  3. You can prepare this in advance for up to a day. Cover the casserole dish with aluminum foil and refrigerate. Add 5 minutes or so cooking time to compensate for the fact that the Spinach Gratin is cold from the refrigerator.
  4. The leftovers are as good, if not better. I generally just heat the leftovers for several minutes in the microwave.


Calories: 201kcal | Carbohydrates: 15g | Protein: 12g | Fat: 11g | Saturated Fat: 7g | Cholesterol: 30mg | Sodium: 651mg | Potassium: 565mg | Fiber: 4g | Sugar: 6g | Vitamin A: 13652IU | Vitamin C: 10mg | Calcium: 397mg | Iron: 2mg