The joys of white fish with mustard sauce
10 September 2018
It’s the simplest thing in the world. A meaty white fish. A delicious creamy Dijon mustard sauce. Marriage made in heaven. A more common variant of this would be to have the fish with Dijonnaise sauce - which is the same principle but the sauce has a base of mayonnaise rather than this one which is just a simple cream sauce. Either way, it’s the mustard that makes it sing.
I often cook halibut this way - indeed, it’s my favourite way to eat it. But medallions of monkfish tail do very nicely as well, and in this case we’re talking some sustainably-sourced cod loin. Poach or pan-fry the fish until just cooked, flaking and meltingly soft. Place them on a bed of crushed steamed new potatoes and some garden peas. Pour some of the mustard sauce over the veg before placing the fish on top, and then a little more on top of the fish for good measure.
If you’re poaching the fish, you really need to make what’s called a court bouillon to use as the poaching liquid. Take 1 litre of water, 60g of white wine vinegar, 2 onions thinly sliced, 1 celery stick sliced, 1 carrot sliced, a Bouquet Garni and salt and pepper. Combine them all in a pot and simmer for 30 minutes before straining and using to poach your fish.
I do like to poach the fish since you get a lovely moist finish and bags of flavour. In this case, however, I was in a hurry. Sometimes compromises have to be made. So some simple pan frying was in order. So long as you’re watching the cooking like a hawk, ready to pounce as soon as the fish is opaque and flakes when teased with a fork, then you still get a lovely moist fish. That’s the main part of the struggle right there.
My go-to mustard sauce is very simple - about 25g of butter melted in a small frying pan, then about 100ml double cream added and gently cooked until it’s bubbling and starting to thicken. Add a good dollop of Dijon mustard - some will tell you a teaspoon or two, but I go for at least a tablespoon - and then taste and add salt and pepper and taste again. Once the salt is at the right level, you can make it sing even more with just a squeeze of lemon juice or, if you don’t have any lemons, a small glug of white wine vinegar.
You don’t need me to tell you how to steam or boil new potatoes and frozen garden peas. I just cooked the potatoes to soft, crushed them lightly with a potato masher and seasoned them, then mixed them with the cooked peas and put a little mound of them on the plate. A nice helping of sauce onto that, followed by the fish, followed by more sauce. Hand it over and wait for sighs of simple joy.
If you want to make the sauce just a little more sophisticated, fry some finely chopped shallot in oil and butter at the start and then add half a glass of white wine. Once that has nearly evaporated, add more butter and the cream, and then the mustard. Taste again and season - the wine should provide some acidity so you may not need the lemon juice to season, but go by the taste. Then soon before serving, stir in some chopped tarragon. Delicious.