Name: Stupka – Kashubian herring sauce with potatoes
Prep time: 30 min
Cook time: 30 min
Total time: 180 min
Yield: 4 servings
Cuisine: Polish
Ingredients: 500 g refrigerated commercial salt-cured herring fillets; 1 L cold water, for soaking; 40 g unsalted butter; 180 g yellow onion, finely diced; 35 g plain wheat flour; 350 ml water; 50 ml clean commercial herring packing brine; 1 small bay leaf (about 0.2 g); 2 allspice berries (about 0.5 g); 0.5 g ground black pepper; Fine salt, only if needed after tasting (up to 1 g); 800 g waxy potatoes

A rustic bowl of thick Kashubian herring sauce with potato, onion and herring on a linen-covered table.

Yield 4 servings

Serving size about 240 g sauce with roughly 200 g boiled potatoes

Prep time 30 minutes active, plus at least 2 hours to soak the herring

Cook time 30 minutes

Ingredients ↓

Recipe at a glance

Stupka – Kashubian herring sauce with potatoes

Stupka is a thick, pourable Kashubian sauce of herring and onion, traditionally associated with a toasted-flour thickener. This measured home version uses salt-cured herring, butter and boiled potatoes; the regional listing describes the dish but does not publish an exact formula.

In Kashubia, a coastal region of northern Poland, herring has long been an important preserved fish. The Pomorskie entry for Stupka – sos śledziowy na zaklepce describes a gray-brown sauce with visible pieces of herring and onion, a savoury fish-and-onion taste and the aroma of toasted flour. The herring pieces are small, about 1 cm across, and the sauce is thick enough to pour.

The name stupka is associated in Kashubian dialect with a flour-thickened sauce made in a pan, using butter, rendered fat or herring liquid. The registered description supports the dish’s regional identity and sensory character, but it does not give exact proportions or a household method. This recipe is therefore a practical measured adaptation, not a claim to reproduce one definitive original.

Here, salted herring is soaked under refrigeration to make its salt level more manageable, then folded into a smooth onion sauce thickened with toasted flour. A little clean commercial herring brine deepens the flavour; the sauce is served over boiled potatoes for a filling meal. Because salt-cured fish varies considerably, taste before adding any extra salt.

Tips for success

Salt-cured herring varies by brand and cut. Soak it in the refrigerator for at least 2 hours, change the water once, then taste a small piece after draining. If it remains too salty, continue soaking in fresh cold water and check again.
Discard the soaking water. Use only clean brine from the commercial herring package, and start with no added salt.
Toast the flour gently in the butter and onion until it smells nutty and turns pale beige. Keep stirring so it thickens the sauce without scorching.
Whisk the water in gradually before adding the brine. This helps make a smooth sauce rather than floury lumps.
Cut the herring into pieces about 1 cm across, as described for the regional dish. Simmer gently so the pieces stay intact.
Check the thickest herring piece with an instant-read thermometer; it should reach at least 63 °C. A rolling boil can break up the fish and make the sauce look rough.

Ingredients

Herring and soaking

500 g refrigerated commercial salt-cured herring fillets
1 L cold water, for soaking

Herring sauce

40 g unsalted butter
180 g yellow onion, finely diced
35 g plain wheat flour
350 ml water
50 ml clean commercial herring packing brine
1 small bay leaf (about 0.2 g)
2 allspice berries (about 0.5 g)
0.5 g ground black pepper
Fine salt, only if needed after tasting (up to 1 g)

To serve

800 g waxy potatoes

Method

Directions

Desalt and prepare the herringKeep the herring refrigerated. Place it in a clean covered bowl, add 1 L cold water and soak for 2 hours in the refrigerator at or below 4 °C. Change the water once after 1 hour. Taste a small piece; if it is still too salty, continue soaking in fresh refrigerated water and taste again. Discard all soaking water. Drain the fish, remove any skin and bones, and cut it into pieces about 1 cm across.
Boil the potatoesScrub or peel the potatoes and cut any large ones into even pieces. Put them in a medium saucepan and cover with fresh water. Bring to a boil, then simmer for 15–20 minutes, until a knife slides easily into the centre. Drain and keep warm.
Soften the onionMelt the butter in a wide, heavy saucepan over medium-low heat. Add the onion and cook for 8–10 minutes, stirring often, until soft and translucent. Do not brown it deeply.
Toast the flour and make the sauceSprinkle in the flour and stir continuously for 2–3 minutes, until the paste smells toasted and turns pale beige. Gradually whisk in 350 ml water until smooth, then stir in the clean herring brine. Add the bay leaf, allspice and black pepper. Simmer gently for 4–5 minutes, until the sauce is thick enough to coat a spoon.
Cook the herring throughAdd the diced herring and stir gently. Keep the sauce at a gentle simmer for 2–4 minutes, until the thickest fish pieces reach at least 63 °C. Avoid a rolling boil so the pieces keep their shape. Remove the bay leaf and allspice. Taste, then add up to 1 g salt only if needed. The finished sauce should be thick but pourable, with visible herring and onion pieces.
ServeSpoon the hot sauce over the warm potatoes and serve promptly.

Nutrition per serving

Energy430 kcal
Carbohydrate44 g
Protein22 g
Fat18 g
Fibre4 g
Sodium1,000 mg
Allergensfish (herring), wheat (gluten), milk (butter)

Approximate values for one of four servings, including about 200 g potatoes: Nutrition is an estimate based on generic ingredients. Salt remaining in the herring depends on the product and soaking time, so sodium may vary widely. The estimate includes the listed sauce and potatoes but not additional salt.

Serving, make-ahead, and storage: Serve the sauce generously over boiled waxy potatoes. Its savoury, salty flavour needs little more; a simple cucumber salad or steamed vegetables can round out the meal without competing with the herring.

Serving, make-ahead, and storage: You can soak and prepare the herring ahead, but keep it covered in the refrigerator at or below 4 °C and discard the soaking water. For the best texture, make the sauce shortly before serving. Do not leave cooked fish sauce at room temperature for more than 2 hours.

Serving, make-ahead, and storage: Refrigerate leftovers in a shallow covered container within 2 hours. Keep them at or below 4 °C and use within 3–4 days. Reheat gently, stirring carefully, until the centre reaches 74 °C. Add a spoonful of water if the sauce has thickened in the refrigerator.

Frequently asked questions

Is this an exact historical recipe?

No. The Pomorskie listing describes the dish’s region, appearance and flavour, but does not provide measured quantities. This version gives a repeatable home method while keeping the defining herring, onion and toasted-flour sauce.

Can I use fresh herring instead?

Fresh herring will not have the same salty, preserved flavour. This recipe is designed for commercial salt-cured fillets. If you use another product, follow its storage instructions and season only after cooking and tasting.

Why is my sauce too salty?

Salt-cured fish varies, and the packing brine adds more salt. Soak the fish longer in fresh refrigerated water, discard that water, and do not add salt until the sauce is finished. If needed, loosen a salty sauce with a little hot water and serve it with extra plain potato.