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Parmesan Spinach Gratin with Buttery Panko Breadcrumbs

Parmesan spinach gratin combines creamy spinach filling with a buttery panko and Parmesan topping. Baked until bubbling at the edges and golden brown, it makes a comforting, crisp-topped side dish.
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Prep Time 15 minutes
Cook Time 35 minutes
resting 10 minutes
Total Time 1 hour
Servings: 6 servings
Course: Side Dish
Cuisine: American
Calories: 330
Ingredients Equipment Method Notes

Ingredients
  

For the spinach gratin
  • 1 cooking spray for coating
  • 2 package (10 oz) frozen chopped spinach thawed and squeezed very dry
  • 4 tbsp unsalted butter divided; 2 tablespoons for the filling and 2 tablespoons for the topping
  • 0.5 cup yellow onion finely chopped
  • 1 cloves garlic minced
  • 2 tbsp all-purpose flour
  • 1 cup whole milk
  • 0.5 cup heavy cream
  • 0.5 tsp kosher salt
  • 0.25 tsp black pepper
  • 0.125 tsp ground nutmeg
  • 0.75 cup Parmesan cheese finely grated, divided; 1/2 cup for the filling and 1/4 cup for the topping
For the buttery panko topping
  • 0.75 cup panko breadcrumbs

Equipment

  • 1 8-inch square baking dish
  • 1 10-inch skillet

Method
 

Make the spinach filling
  1. Preheat the oven to 375°F.
  2. Lightly coat an 8-inch square baking dish with cooking spray.
  3. If needed, squeeze the thawed spinach in handfuls over the sink until no liquid drips from it.
  4. Melt 2 tablespoons of the butter in a 10-inch skillet over medium heat.
  5. Add the onion and cook for 4–5 minutes until softened.
  6. Stir in the garlic for 30 seconds.
  7. Sprinkle in the flour and stir for 1 minute.
  8. Gradually whisk in the milk and cream.
  9. Add the salt, pepper, and nutmeg and cook for 3–5 minutes, whisking, until the sauce thickens enough to coat the back of a spoon.
  10. Remove the skillet from the heat and stir in 1/2 cup of the Parmesan and the spinach.
  11. Spread the mixture in the prepared baking dish.
Make the topping
  1. Melt the remaining 2 tablespoons of butter in a small microwave-safe bowl for 15–30 seconds.
  2. Stir in the panko and remaining 1/4 cup Parmesan.
Bake the gratin
  1. Sprinkle the panko mixture evenly over the spinach filling.
  2. Bake for 20–25 minutes until bubbling at the edges and golden brown on top.
  3. Let rest for 10 minutes before serving.

Notes

Squeeze the spinach very dry so the gratin stays creamy rather than watery. Refrigerate leftovers for up to 3 days; freezing is not recommended because the creamy sauce may separate. For a gluten-free version, use gluten-free flour and gluten-free panko.