Ingredients

Equipment Needed

• •Fish kettle or wide deep pan (large enough to hold 4 trout in a single layer)
• •Slotted spoon or fish slice
• •Kitchen string or toothpicks for curving the trout
• •Small saucepan for melting butter
• •Fine grater for horseradish

Instructions

1. 1

   Choose your trout

   This recipe begins at the fishmonger, not at the stove. You need trout that has never been frozen, never been sealed in plastic, and ideally was alive that morning. The natural slime coating on the skin is what turns blue when it meets the vinegar. If the fish has been handled too much, rinsed, or stored on ice for days, that coating is gone and the bluing will not happen. Tell your fishmonger you need the fish whole and untouched, gutted through the gills if possible to keep the belly intact. Eyes should be clear, gills bright red, and the fish should smell like a clean river. Nothing else.

   If you can buy live trout from a fish farm, that's the gold standard. Many Austrian Gasthäuser keep their own trout ponds for exactly this reason. The shorter the journey from water to pot, the more vivid the blue.
2. 2

   Build the court-bouillon

   Combine the cold water, white wine, onion, carrot, parsnip, bay leaf, peppercorns, allspice berries, salt, parsley sprigs, and lemon slices in a wide, deep pan or fish kettle. You want a vessel broad enough to hold all four trout in a single layer without stacking them. Bring the liquid to a gentle boil and let it simmer for fifteen minutes. The vegetables and aromatics need time to release their flavor into the water. This is your Sud, your court-bouillon, and it does most of the seasoning work for the fish.

   A Grüner Veltliner is perfect here. Its white pepper and green apple notes complement trout beautifully. If you don't have Austrian wine, any clean, dry white will do. Save a glass for yourself while you cook.
3. 3

   Start the potatoes

   While the court-bouillon simmers, place your potatoes in a pot of cold salted water and bring to a boil. Cook until a knife slides through with no resistance, about twenty minutes depending on size. Drain them, peel if you like (I leave the skins on for Kipfler), and toss with a generous knob of butter and chopped parsley. Keep them warm under a lid.

4. 4

   Prepare the trout

   Handle the fish as little as possible. Every time you touch it you disturb the slime layer. Lay each trout on a large plate or tray. Curve the fish gently so the tail nearly meets the head, like a crescent. You can tie it loosely with kitchen string if it won't hold the shape. This curl is traditional and also practical: it helps the fish fit in the pan and cook evenly.

   Some cooks pierce a toothpick through the tail and the jaw to hold the curve. This works well and makes handling easier when you lift the cooked fish out of the liquid.
5. 5

   Apply the vinegar

   This is the moment that gives the dish its name. Heat 150ml of white wine vinegar until it's just below boiling. Slowly ladle or pour the hot vinegar over each trout, making sure it coats the skin evenly on all sides. You'll see it happen almost immediately: the slime reacts with the acid and the skin turns a ghostly, iridescent blue-grey. It's one of the most beautiful things a kitchen can show you. If the color doesn't come, your fish wasn't fresh enough. There's no fix for that.

6. 6

   Poach the trout

   Remove the court-bouillon from the heat. It should be hot but not bubbling. Gently lower the vinegar-dressed trout into the liquid. The fish should be fully submerged. If the liquid doesn't cover them, add a splash of hot water. Let the trout poach off the heat for eight to twelve minutes, depending on their size. The liquid should never return to a boil. You'll know the fish is done when the dorsal fin pulls away easily with a gentle tug and the flesh near the backbone is opaque and just beginning to flake.

   Poaching off the heat is the whole secret. If the water boils, the skin tears, the flesh tightens, and the blue color fades. You want the gentlest possible cooking. Patience again.
7. 7

   Melt the butter

   While the trout poaches, melt the butter in a small pan over low heat. Let it warm until it's fully liquid and just starting to foam, but don't let it brown. This is Zerlassene Butter, melted butter, not Nussbutter. You want it golden and clear, not nutty. Pour it into a warm serving jug or small bowl.

8. 8

   Plate and serve

   Lift each trout carefully from the court-bouillon using a slotted spoon or fish slice and let it drain for a moment. Place it on a warm plate, still curved, with the blue skin facing up. Arrange the parsley potatoes alongside. Set the melted butter and freshly grated horseradish on the table in separate dishes. Lemon wedges on the side. The diner spoons the hot butter over each forkful and takes the horseradish in whatever quantity they please. That's it. No sauce, no reduction, nothing between you and the trout. Mahlzeit!

Chef Tips

• •The single most important thing is freshness. I cannot say this enough. If your fishmonger can't guarantee the trout was caught that day, make something else. Buy a piece of salmon and roast it. Don't attempt Forelle Blau with yesterday's fish. You'll just have a grey, sad-looking poached trout and you'll wonder what the fuss was about.
• •Grate the horseradish fresh at the table if you can. The moment you grate it, it starts losing its bite. Prepared horseradish from a jar works in a pinch, but the difference between fresh and jarred is the difference between a shout and a whisper.
• •In Austria, this dish is often served with a small bowl of the strained court-bouillon on the side. The broth picks up flavor from the fish and the aromatics and becomes a delicate little soup in its own right. Offer it to your guests in small cups. It's a lovely detail.
• •Gretel always said that Forelle Blau separates cooks who respect ingredients from cooks who just follow recipes. You can't technique your way out of a bad fish.

Advance Preparation

• •The court-bouillon can be made a day ahead and refrigerated. Reheat it gently before using, but don't bring it back to a rolling boil.
• •Potatoes can be boiled up to an hour ahead and kept warm in their pot with the lid on.
• •The trout itself cannot be prepared in advance. Buy it the day you cook it. The bluing only works with the freshest possible fish, and there are no shortcuts around that.

Frequently Asked Questions

Nutrition Information

1 serving (about 430g)