📝 About This Recipe
This elegant French-inspired classic features succulent white fish nestled on a vibrant bed of garlicky sautéed spinach, all enveloped in a velvety, nutmeg-scented Mornay sauce. It is a quintessential seafood bake that balances the earthiness of greens with the luxurious richness of melted Gruyère cheese. Perfect for a sophisticated dinner party or a comforting weekend meal, this dish celebrates the timeless marriage of 'Florentine' style greens and delicate coastal flavors.
🥗 Ingredients
The Fish & Spinach Base
- 1.5 lbs Sea Bass or Cod Fillets (cut into 4 equal portions, patted dry)
- 16 oz Fresh Baby Spinach (washed and stems removed)
- 3 cloves Garlic (minced)
- 1 tablespoon Unsalted Butter (for sautéing spinach)
- 1 tablespoon Lemon Juice (freshly squeezed)
The Mornay Sauce
- 3 tablespoons Unsalted Butter
- 3 tablespoons All-Purpose Flour
- 2 cups Whole Milk (warmed slightly)
- 1 cup Gruyère Cheese (freshly grated)
- 1 teaspoon Dijon Mustard
- 1/4 teaspoon Ground Nutmeg (freshly grated is best)
- to taste Kosher Salt & White Pepper
The Topping & Garnish
- 1/2 cup Panko Breadcrumbs
- 1/4 cup Parmesan Cheese (finely grated)
- 2 tablespoons Fresh Parsley (finely chopped)
- 1/2 teaspoon Paprika (for color)
👨🍳 Instructions
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1
Preheat your oven to 400°F (200°C) and lightly grease a 9x13 inch ceramic baking dish or gratin dish with butter.
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2
In a large skillet over medium heat, melt 1 tablespoon of butter. Add the minced garlic and cook for 30 seconds until fragrant.
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3
Add the spinach to the skillet in batches, tossing until wilted. Once wilted, transfer the spinach to a fine-mesh sieve and press firmly with a spoon to remove as much liquid as possible. This prevents a watery bake.
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4
Spread the squeezed spinach evenly across the bottom of the prepared baking dish. Sprinkle with a pinch of salt and a squeeze of lemon juice.
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5
Season the fish fillets on both sides with salt and white pepper. Arrange them in a single layer on top of the bed of spinach.
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6
Prepare the roux: In a medium saucepan, melt 3 tablespoons of butter over medium heat. Whisk in the flour and cook for 1-2 minutes until it smells nutty but remains pale.
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7
Slowly pour in the warmed milk, whisking constantly to ensure no lumps form. Continue to cook and whisk until the sauce thickens enough to coat the back of a spoon.
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8
Remove the sauce from heat. Stir in the Dijon mustard, nutmeg, and 3/4 cup of the Gruyère cheese until melted and smooth.
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9
Pour the Mornay sauce evenly over the fish fillets, ensuring they are well covered to keep them moist during baking.
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10
In a small bowl, mix the Panko breadcrumbs, the remaining Gruyère, Parmesan, and paprika.
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11
Sprinkle the breadcrumb mixture over the sauce. This will provide a beautiful golden crunch.
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12
Bake for 15-18 minutes, or until the fish is opaque and flakes easily with a fork. The sauce should be bubbling at the edges.
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13
Turn the broiler on for the last 1-2 minutes to achieve a deep golden-brown crust on the topping, watching closely to prevent burning.
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14
Remove from the oven and let rest for 5 minutes. Garnish with fresh parsley and serve immediately.
💡 Chef's Tips
Squeeze the spinach vigorously; excess moisture is the enemy of a perfect gratin. Use white pepper instead of black in the sauce to maintain a pristine, creamy aesthetic. If using frozen fish, ensure it is completely thawed and patted very dry with paper towels. For an extra touch of luxury, add a splash of dry white wine to the spinach while sautéing. Freshly grated nutmeg makes a world of difference compared to pre-ground powder.
🍽️ Serving Suggestions
Serve alongside buttery roasted fingerling potatoes to soak up the extra sauce. A crisp, chilled glass of Sauvignon Blanc or Chablis cuts through the richness beautifully. Pair with steamed asparagus or a light cucumber salad for a refreshing contrast. Offer crusty French baguette slices for cleaning the plate. A simple garnish of lemon wedges provides a bright acidity to balance the cheese.