Fish in Mustard Sauce

Chef's elaboration

This works because everything is built on softness, but does not become bland. Leek adds sweetness, milk rounds out the fish, coarse mustard cuts straight through it, and dill keeps the whole thing light. The smart move is to poach in the leek milk itself; that gives you a sauce that really tastes like fish instead of like loose mustard with cream.

Technique spotlight

Poaching is everything here. The milk should only tremble, never boil. If you see small ripples at the edge and a little steam, you are doing it right. Lay the fish in a single layer, spoon some warm milk over the top, and then touch it as little as possible. Restaurant quality comes from control, not higher heat.

Pairing notes

Drink a Muscadet Sèvre-et-Maine sur lie with this, cold but not ice-cold. Beer also works: a fresh wheat beer with low bitterness. Alcohol-free, choose cold jasmine tea with a squeeze of lemon; it surprisingly picks up the dill and mustard well.

Storage notes

Honestly, this is best straight from the pan. Reheating is possible, but only gently over low heat; otherwise the sauce splits and the fish dries out. Keep for at most 1 day in the refrigerator. Keeping the potatoes separate helps. Freezing is not a good idea; the creamy mustard sauce turns sad.

Chef's critique

Most home cooks let the milk boil and end up with dry, falling-apart fish and a grainy sauce. Second mistake: too much mustard, then all you taste is sharpness. Keep the pan below a simmer and dose mustard as if it were an herb, not a main ingredient.

Suggestions

I prefer floury potatoes here rather than waxy ones; they catch sauce better. Cod is good, but haddock or pollock is often juicier and cheaper. At the end, add a knob of cold butter to the sauce for shine. And wash the leek obsessively; sand in a delicate sauce is unforgivable.

Ingredients

• 500 g Potato
• 2 pcs Leek
• 30 g Butter
• 300 g Cod fillet
• 400 ml Whole milk
• 1 pcs Bay leaf
• 0.5 tsp Black pepper
• 2.75 tsp Kosher salt
• 2 tbsp Wholegrain mustard
• 10 g Dill
• 1 pcs Lemon

Method

1. Put {potato} in a medium saucepan with cold water and {kosher_salt}. Bring to a boil over medium heat and cook until tender and easily pierced with a knife.
2. Slice {leek} into thin rings, pick and chop {dill} finely, and cut {lemon} into wedges.
3. Melt {butter} in a wide sauté pan over low heat. Add {leek} with a pinch of {kosher_salt} and sweat gently until the leek is soft, glossy, and smells sweet without coloring.
4. Pat {cod_fillet} dry so it cooks evenly. Pour {whole_milk} into the sauté pan with the {leek}, add {bay_leaf}, {black_pepper}, and some {kosher_salt}, and heat over low heat until the milk just trembles. Lay {cod_fillet} in it and poach very gently until the fish is opaque and flakes easily.
5. Lift {cod_fillet} carefully from the pan and keep warm. Remove {bay_leaf}, set the pan over medium heat, and reduce the poaching liquid briefly until it lightly thickens and looks silky. Stir in {wholegrain_mustard} and most of the {dill}, taste, and season with {kosher_salt} and a squeeze of {lemon}.
6. Drain {potato} and divide among warm plates. Spoon the {leek} and sauce alongside, place {cod_fillet} on top, and finish with the rest of the {dill} and another small squeeze of {lemon} for freshness.