Ingredients:

  • 4 (175g / 6 oz each) thick-cut fillets of Cod, Haddock, or Halibut (skinless and boneless)
  • 1 Tbsp (15 ml) Olive Oil
  • 1/2 tsp (3g) Kosher Salt (divided)
  • 1/4 tsp (1g) Black Pepper (freshly ground, divided)
  • 450g (16 oz) Fresh Spinach (or 250g/9 oz frozen, thawed and drained)
  • 1 clove Garlic, minced
  • 4 Tbsp (56g) Unsalted Butter
  • 4 Tbsp (30g) All-Purpose Flour
  • 500 ml (2 cups) Whole Milk, warmed slightly
  • 1/4 tsp (1g) Nutmeg, freshly grated
  • Pinch of Cayenne Pepper (optional)
  • 1/2 tsp (3g) Kosher Salt
  • 1/4 tsp (1g) White Pepper
  • 75g (3 oz) Gruyère Cheese, grated
  • 25g (1 oz) Parmesan Cheese, finely grated

Instructions:

  1. Preheat your oven to 200°C (400°F). Lightly grease the baking dish.
  2. Pat the cod fillets dry with paper towels. Season both sides generously with salt and pepper. Set aside.
  3. Heat olive oil in a large skillet. Add the minced garlic and sauté quickly (about 30 seconds). Add the fresh spinach and wilt down entirely.
  4. Transfer the wilted spinach to a colander. Once slightly cooled, gather the spinach and squeeze out all excess liquid using a clean kitchen towel or cheesecloth. This step is crucial to prevent a watery final dish.
  5. Spread the well-drained spinach evenly over the bottom of the prepared baking dish. Place the seasoned fish fillets on top of the spinach bed.
  6. Create the Roux: Melt the butter in a medium saucepan over medium heat. Whisk in the flour and cook, stirring constantly, for 1–2 minutes until the roux is pale gold and smells slightly nutty.
  7. Add Milk: Gradually whisk in the warm milk, a little at a time, ensuring the mixture remains completely lump-free. Once all the milk is added, continue whisking until the sauce thickens enough to coat the back of a spoon (about 5–7 minutes). Reduce heat to low.
  8. Season and Finish Béchamel: Remove the sauce base from the heat. Stir in the nutmeg, cayenne, salt, and white pepper.
  9. Turn into Mornay: Stir in the Gruyère and Parmesan cheese until melted and the sauce is smooth and glossy. Taste and adjust seasoning.
  10. Assemble: Pour the silky Mornay sauce evenly over the fish fillets and spinach, ensuring the fish is completely covered.
  11. Bake in the preheated oven for 18–22 minutes. The cooking time will depend slightly on the thickness of your fillets.
  12. Check Doneness: The fish is done when it is opaque throughout and flakes easily with a fork (internal temperature should reach 63°C / 145°F).
  13. Optional Broil Finish: For a deeper golden color, switch the oven to the grill (broiler) setting for the last 1–2 minutes, watching carefully to prevent burning.
  14. Rest and Serve: Allow the dish to rest for 5 minutes before serving.