Fried Herring in Onion Sauce

Name: Fried Herring in Onion Sauce
Prep time: 35 min
Cook time: 30 min
Total time: 65 min
Yield: 4 servings personer
Cuisine: danish
Ingredients: 700 g fresh herring fillets, cleaned, as butterflied fillets; 100 g rye flour; 1 tsp salt; ½ tsp pepper, freshly ground; 75 g butter; 40 g butter; 3 onions, thinly sliced into half-moons; 3 tbsp all-purpose flour; 5 dl whole milk; salt; pepper; 1 kg potatoes, scrubbed; 2 tsp salt, for the cooking water; ½ bunch fresh parsley, chopped

A Danish classic: herring fillets breaded in rye flour and fried until crisp, served with a creamy onion sauce of sautéed onions and milk, plus potatoes.

🍽️ 4 servings personer⏱️ 1 h 5 min (35 min active)danish

Put the potatoes on first, while the onions slowly turn sweet and form the base of the creamy onion sauce. Don't fry the herring until the sauce is done and being kept warm, so the crust reaches the plate perfectly crisp. The smooth, creamy onion sauce is the dish's main anchor.

Ingredients

The Herring

700 g fresh herring fillets, cleaned, as butterflied fillets
100 g rye flour
1 tsp salt
½ tsp pepper, freshly ground
75 g butter

The Onion Sauce

40 g butter
3 onions, thinly sliced into half-moons
3 tbsp all-purpose flour
5 dl whole milk
salt
pepper

Sides and Serving

1 kg potatoes, scrubbed
2 tsp salt, for the cooking water
½ bunch fresh parsley, chopped

How to make it

Put the scrubbed potatoes in a pot with cold water, just enough to cover them, and add the 2 tsp salt. Bring the water to a boil and cook the potatoes for about 30 minutes from cold water, until a sharp knife slides easily into the center without resistance. ⏱ 30 min · passive
Melt the 40 g butter in a heavy-bottomed pot over medium heat. Sauté the onions for 10-12 minutes, stirring occasionally, until completely soft and light golden and have lost their raw sharpness. ⏱ 10 min
Chef's tip Keep them at a quiet sizzle, translucent and barely golden. Onions pushed hard over high heat catch at the edges, and those scorched flecks read as bitterness in a pale milk sauce with nowhere to hide.
Sprinkle the flour over the onions and stir for 2 minutes, until the flour has been fully absorbed into the butter and smells faintly nutty — this brief cooking is what removes the raw flour taste from the sauce.
Chef's tip Stop at pale and sandy with a faint biscuit smell. The further a roux browns, the less thickening power the flour retains — a dark one needs noticeably more to reach the same body.
Add the whole milk a little at a time while whisking constantly, so the sauce becomes completely smooth between each addition. Let it simmer for 8-10 minutes, stirring occasionally, until it's creamy and flows slowly off the spoon. Season to taste with salt and pepper, and keep it warm over low heat. ⏱ 8 min–10 min
Pat the herring fillets completely dry on both sides, so the rye flour can adhere instead of sliding off in the pan. Mix the rye flour with 1 tsp salt and the freshly ground pepper on a flat plate. Turn only half of the fillets in the flour mixture and shake off the loose flour, so the coating is thin and even; leave the rest lying dry and flour them the same way just before they go into the pan, so the coating doesn't draw moisture and turn gummy while they wait.
Heat a large pan over medium-high heat and melt half of the 75 g butter, until it foams up vigorously and the foam has just subsided again.
Chef's tip The foam is water boiling out of the butter. When it subsides the pan is at its hottest before the milk solids darken — that's the window. If the butter has gone deep brown, wipe the pan and start the second batch fresh.
Place half of the floured fillets in the pan skin-side down and fry them for 3 minutes, until the rye flour crust is dark golden and releases from the pan on its own.
Chef's tip Leave them alone and fry in two batches with space between. A crowded pan drops in temperature and the released moisture steams the crust soft; the fillet lifts freely once it has browned, so early sticking means it isn't ready.
Turn the fillets and fry them for another 2 minutes, until the flesh is white and firm all the way in along the backbone line. Fry the remaining fillets the same way in the last of the 75 g butter.
Chef's tip Herring fillets are thin and go from succulent to stringy in seconds. Lift them out the moment the flesh has just turned opaque and pulls away from the line of the backbone under light pressure — they carry on cooking a little on the plate.
Place two warm herring fillets on each flat plate and pour the warm onion sauce over the fish. Set the boiled potatoes alongside and sprinkle the chopped parsley over the sauce.