Ingredients:

  • 4 fillets (about 6 oz / 170g each) skinless, firm white fish (e.g., Cod, Haddock, or Halibut)
  • 1 tsp Kosher Salt, divided
  • ½ tsp freshly cracked Black Pepper, divided
  • 1 Tbsp Olive Oil
  • 2 lbs (900g) Fresh Spinach (or 16 oz / 450g frozen, thawed and squeezed)
  • 2 Tbsp Unsalted Butter (for spinach)
  • 2 cloves Garlic, minced
  • Pinch of Nutmeg (optional)
  • 3 Tbsp Unsalted Butter (for roux)
  • 3 Tbsp All-Purpose Flour
  • 2 cups Whole Milk, warmed
  • 1/4 tsp White Pepper
  • ½ tsp Kosher Salt (or to taste)
  • 4 oz (115g) Gruyère or sharp white Cheddar cheese, grated
  • 2 Tbsp finely grated Parmesan cheese (for topping)

Instructions:

  1. Preheat Oven: Set oven temperature to 400°F (200°C). Lightly grease a 9x13 inch baking dish.
  2. Prep Fish: Pat fish fillets very dry and season generously with the divided salt and pepper. Set aside.
  3. Wilt Spinach: Melt 2 Tbsp butter in a large skillet over medium heat. Add minced garlic and sauté briefly (30 seconds). Add spinach and wilt until completely softened.
  4. Remove Moisture (Crucial Step): Transfer the wilted spinach to a fine-mesh sieve or colander. Crucially, squeeze out all excess moisture using the back of a spoon or a clean tea towel. If the spinach is wet, the final dish will be watery.
  5. Lay Base: Spread the dried, seasoned spinach evenly across the bottom of the prepared baking dish.
  6. Start the Roux: In a medium saucepan, melt 3 Tbsp butter over medium heat. Whisk in the flour until smooth (the roux). Cook for 1-2 minutes, stirring constantly, until pale golden and fragrant.
  7. Add Milk: Gradually whisk in the warm milk, a little at a time, ensuring no lumps form. Continue to whisk vigorously until the sauce thickens enough to coat the back of a spoon (about 5-7 minutes).
  8. Season and Add Cheese: Remove the Béchamel from the heat. Stir in salt, white pepper, and the grated Gruyère/Cheddar cheese until melted and smooth. This is now your Mornay sauce. Taste and adjust seasoning.
  9. Assemble: Place the seasoned fish fillets directly on top of the spinach base in the baking dish.
  10. Smother: Pour the Mornay sauce evenly over the fish and spinach, ensuring the fillets are well covered.
  11. Final Touch: Sprinkle the Parmesan cheese and a small pinch of nutmeg over the top of the sauce.
  12. Bake: Bake for 18-22 minutes, or until the fish is flaky, opaque, and cooked through (internal temperature of 145°F / 63°C), and the sauce is golden brown and bubbling merrily.
  13. Rest and Serve: Allow the Baked Fish Florentine to rest for 5 minutes before serving.