Creamy Seafood Gratin: Not A Humble Pie

Creamy seafood gratin takes the deeply satisfying notion of comfort food to a higher level. A trio of creamily spiced seafood is crowned by buttery mashed potatoes, flavored with garlic and Parmesan and a spark from red serrano peppers. Calling it a pie somehow seems like a put-down.

At a supper party almost forty years ago, I was introduced to a simpler version of this seafood gratin dish. I was head-over-heels on our first encounter. And we have stayed together very happily through those many years. I might not have improved with the passage of time, but a dish I love and enjoy tweaking certainly has.

As with so many great recipes, fairly ordinary ingredients here are transformed into something super special. This recipe is down-to-earth and just plain decent. But at the same time, it’s sophisticated and elegant. That’s a rare combination.

Creamy seafood gratin
Creamy seafood gratin, plated and ready to serve

The seafood trio in our seafood gratin

First, there’s a white, non-oily fish like hake, cod, or Alaskan pollock. Second, the contrast of a lightly smoked fish — haddock would be a good, non-oily choice. And then a generous amount of shell-on, headless prawns or shrimp, in a sort of medium size at about two-and-a half inches long.

The trio gets cooked very gently — so you’ll be maxing the individual flavors and textures. That’s important, but it’s just one of the many delights this seafood gratin recipe delivers.

For all three, fresh would be ideal, but frozen is grand because they each freeze really well and — de-frosted — that’s what I most often use.

The seafood’s flavors and textures are all delicate, and that’s why they’re cooked in a way that will protect them. That begins with a very light poaching. This gives the fish just enough heat, so it can be broken into handsome chunks. The prawns get a similar treatment. The trio finishes its cooking in your oven after it has been sauced and topped.

The sauce

By comparison, the sauce is very different indeed. It’s rich, complex, and deep, with some surprising, subtle heat and just a little sharply fresh tang.

Those two last qualities come from the spark of a red serrano chili, fresh lemon juice, and capers. Heavy cream, milk, and a little butter add a smooth, rich depth to the sauce. And then its complexity gets extended by dill, tarragon, and parsley.

This is a sauce that can easily stand alone on its merits. But it really shines when it teams up with that seafood.

Creamy seafood gratin
Close-up of creamy seafood gratin, with green peas and buttery mashed potato topping

The crowning glory

That’d be the buttery mashed potatoes, flavored with Parmesan and a little garlic. To max their flavor, the potatoes are boiled with their skins on, along with some crushed garlic. Once peeled, the potatoes are mashed with the garlic, a little butter, some black pepper, and a goodly amount of Parmesan. Result? A topping full of its own individual flavors, textures, and colors — especially since it picks up a little golden crusting from baking in the oven after being lightly sprinkled with paprika.

Overall, this is a dish that can serve many masters. It makes a fine, casual weekend lunch or supper (it’s not fast food), but can also excel as the proud centerpiece of a more structured celebration with family and friends.

However you choose to enjoy it, there’s only one side-dish that — for me at least — can do this dish the justice it deserves. Lightly buttered green peas.

Creamy seafood gratin

Creamy Seafood Gratin

5 from 1 vote
Prep Time 30 mins
Cook Time 1 hr 15 mins
Total Time 1 hr 45 mins
Course dinner
Servings 4 servings
Calories 1113 kcal

Ingredients
 
 

  • 1 red serrano pepper finely chopped, seeds and all
  • 1 pound hake fillets or similar, such as cod or Alaskan pollock. For more flavor, I prefer skin-on fillets.
  • 1 pound smoked haddock fillets or a similar, non-oily, smoked seafish
  • 1/2 pound medium-sized prawns headless, deveined, shell-on
  • 2 1/4 pounds floury potatoes unpeeled
  • 3 cloves garlic peeled and lightly crushed. The cloves should stay pretty much whole, so just crush them lightly.
  • 3 ounces grated parmesan cheese
  • 1 ½ cups whole milk
  • 2 cups heavy cream
  • 2 tablespoons salted butter one for the sauce, one for the potato topping
  • 2 tablespoons plain flour
  • 3 bay leaves
  • 1 heaped tablespoon capers drained and roughly chopped
  • 1 heaped teaspoon dried tarragon I use dried because fresh can be hard to find.
  • 1/2 ounce fresh dill very finely chopped, stalks and all
  • 1 ounce fresh parsley very finely chopped, stalks and all
  • 2 heaped teaspoons ground sea salt
  • 2 heaped teaspoons ground black pepper
  • Paprika for dusting the topping
  • Green peas cooked (for serving on the side and atop for color)

Instructions
 

  • First up, you’ll need a good-sized, ovenproof gratin dish. I used a 14-inch, cast-iron oval one which is about two inches or so deep. A similarly sized ceramic gratin dish is also dandy.
  • Heat your oven to 400F / 200C.

Make the mashed potatoes

  • Put the potatoes and garlic into a medium-sized pan and just cover them with water. Add a heaped teaspoon salt and bring the pan to a boil. As soon as it does, drop the heat to low, cover the pan and let the potatoes cook right through – about ten minutes. Then drain the potatoes and garlic in a big colander, return them both to their pan and set them aside to cool. Do not discard the garlic.
  • Peel the potatoes as soon as they are cool enough to handle. Add a level tablespoon butter, a heaped teaspoon salt, one of black pepper, and all the Parmesan. Now mash the lot until the potatoes are just barely smooth. Cover the pan and set it aside.

Cook the fish

  • Set a big skillet (12-inch is grand) on a medium heat and add the milk, bay leaves, and the two types of fish fillets. As soon as the milk just begins to boil, drop the heat to low. The skillet will be pretty crowded by all the fish, but that’s fine because it means they’ll sit deeper in the milk.
  • You want the fish to poach in the milk at a very gentle simmer – and I mean very gentle – for two minutes on each side. So that’s a total of four minutes at that low simmer. After those four minutes, the poaching is finished and you can turn off the heat.
  • Using a big slotted spoon, remove all the fillets and set them aside in your gratin dish. Leave the milk and the bay leaves in the skillet – that’s important because it’s all going into the sauce.

Make the sauce

  • Melt the butter in a medium-sized saucepan on a low heat. Now add the flour and mix it very thoroughly with the butter on that low heat. Then stir in all the milk from the skillet together with the bay leaves. Keep stirring so that the milk becomes completely combined with the butter and flour mix. Add the heavy cream and stir, stir, stir until you have a completely smooth mixture. You might want to use a small whisk to speed things up a bit, but I just like a wooden spoon.
  • Now, still on that low heat, stir into the creamy sauce the chopped serrano chili, black pepper, capers, and all the tarragon, parsley, and dill. Now add the prawns and, very gently, stir them into the sauce. Continue to cook on low for another three minutes, with the occasional gentle stir so as not to break the prawns. Done. Check for saltiness and adjust accordingly to your taste. Sauce finished.

Bringing it all together

  • Use your fingers to break the fish fillets apart in the gratin dish. You want the pieces to be quite chunky – a sort of big bite size but certainly not smaller. Space the fillets apart so you have a fairly even spread of white fish and smoked fish.
  • Now pour the sauce – with the prawns and bay leaves – over the fish. Stir gently so as not to break the fish apart and to get the prawns evenly spaced across the gratin dish. Time for the topping.
  • Using a dessert spoon, start sliding spoonfuls of the mash onto the sauced seafood. Take some care doing this. You want – as much as possible – for the mash to sit on top, rather than being pressed down into the seafood. Once the dish is evenly covered, use a fork to create furrows right across the top of the mash. Sprinkle on a few pinches of paprika, and put the dish on a high shelf into your pre-heated oven.
  • Let it bake for 35 minutes. The sauce may well bubble out a little around the edges of the dish – that’s fine. And the topping will have taken on some golden crunch. And that really is grand.
  • Serve at once with those lovely green peas.

Notes

And to drink? I like a well-chilled, nicely fruity rosé or perhaps a buttery chardonnay. And those two will give a lot of scope in terms of your own preferences.

Nutrition

Calories: 1113kcalCarbohydrates: 70gProtein: 73gFat: 61gSaturated Fat: 37gTrans Fat: 1gCholesterol: 410mgSodium: 2419mgPotassium: 2369mgFiber: 8gSugar: 11gVitamin A: 4018IUVitamin C: 60mgCalcium: 640mgIron: 7mg

ENVIRONMENTAL INFORMATION

Keyword Serrano Pepper
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UPDATE NOTICE: This post was updated on March 10, 2021 to include new content. It was originally published on March 10, 2021.

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