Fish with mushroom gratin

What is ‘au gratin’ when it’s at home?

I think most people think ‘cheese’ when seeing the word ‘gratin’. Cheesy baked potatoes, vegetables sprinkled with cheese and blasted under the grill – clearly ‘au gratin’ must be another French way of saying cheese!

There is no cheese when it comes to the meaning of the word though. ‘Au gratin’ or ‘gratiné’ comes from the French word ‘gratter’ meaning ‘scratch’ or ‘scrape’. In culinary terms it is used with reference to foods assembled in a shallow dish and baked or grilled, so the surface becomes rough and ‘scratchy’.

Therefore, I think breadcrumbs are a bigger player in gratins than cheese – unless it’s blasted to a crispy crust.

As it often happens, the word ‘gratin’ can also refer to the type of shallow, oval-shaped baking dish that is traditionally used for implementing au gratin recipes.

Popular in many cuisines, especially French and American, gratin or gratiné dishes involve vegetables or meat and fish covered with a blanket of sauce, cheese, breadcrumbs or all at once. They are usually served as a side dish or a main course, depending on the ingredients and the portion size.

As they are rich, creamy and satisfying, there’s also the usual caveat: high in calories, fat and sodium.

But this is where our fish au gratin wins on all fronts: it’s not excessively calorific whilst pleasingly rich and creamy.

It features breadcrumbs but no cheese: cheese and fish are not great together though, as ever, there are exceptions.

What fish for the gratin?

The original NYT recipe says fluke, which is flounder or plaice.

I like to use haddock, turbot or cod but really any thick white fish fillets, preferably skinless, are good to use as long as you don’t overcook them. That’s why thicker, more substantial fish fillets are preferrable as they will take longer to cook, thus allowing the gratin on top to crispen.

What mushrooms for the sauce?

Button mushrooms, white or chestnut, are dainty and elegant but if you can get hold of chanterelles, they’ll make the dish really special.

Either way however, this is the classic ‘easy but impressive’ kind of dish that will have your friends marvelling at your cooking skills and the family wiping the plates clean with relish.

Half the mushroom amount should be chopped very finely, or processed in a blender-chopper or a food processor. The other half will go on top of the dish and needs to be finely sliced.

How to make the sauce

It’s the classic French sauce, starting with shallots softened in butter, with the additions of garlic, finely chopped mushrooms and herbs.

When the aromatics are slightly coloured, liquids go in in the shape of white wine, a little vinegar and some lemon juice. This is then reduced to a thicker consistency and ready to be gratinéed.

The fish fillets, cut into portions if necessary, should sit in a gratin dish in a single layer, on the base of half the sauce.

The rest of the sauce should be spooned over fish, sprinkled with obligatory (for gratin) breadcrumbs and dotted with cold butter.

The dish is baked in very hot oven but still the breadcrumbs might not turn out quite as crisp and crusty as you’d like them.

That’s why I prefer to cook thicker fish this way so that it can spend a little longer in the oven, letting the breadcrumbs ‘gratiner’. You can also switch over to oven grill for the last couple of minutes of the cooking time or use the cook’s blowtorch. Or just ignore this minor shortcoming and enjoy the wonderful flavours.

More elegant fish recipes

Halibut fillet steamed atop braised leeks and carrots, the best cooking method for halibut. Healthy, tasty, and one pan dish to boot!

Fresh mackerel fillets stuffed with samphire, anchovy and breadcrumb mix, grilled and served with parsley butter. Try Tom Kerridge's fantastic recipe for seaside stuffed mackerel.

Miso marinated haddock seared and baked to a succulent, golden beauty. Inspired by Nobu black cod, it is truly an outstanding fish dish.

More gratin recipes

Beetroot gratin, thinly sliced beets baked in garlic and dill infused cream, a gorgeous side to a fish course. No need to pre-cook the beetroot.

Hasselback potatoes with cheese and cream, baked into a crusty gratin. This must be the best potato gratin recipe, made with cheesy hasselbacks - and you don’t need to master the ‘almost slice’ hasselback technique so the recipe is really easy.

Potato and cabbage gratin, herby with sage and dill, cheesy with Gruyere or Cheddar. Rich, warming and absolutely comforting – it’s an oven-baked antidepressant!