Ingredients

   
340g Yukon Gold or red potatoes, sliced 3mm
1 shallot, sliced thin
30g unsalted butter, in bits
340g salmon fillets (2 pieces, skin removed)
4 sprigs dill
1 lemon, zested
30g dry white wine or vermouth
  Salt
  Black pepper

Steps

  1. Heat the oven to 400°F with a rimmed baking sheet inside. Cut two 38cm squares of parchment.

  2. Boil the potato slices in salted water for 2 minutes. Drain and spread on a towel to dry.

  3. Shingle the potatoes into an overlapping oval slightly larger than a fillet, just right of the center of each parchment square. Season with salt and pepper, scatter the shallot, dot with half the butter.

  4. Pat the fillets dry and set one on each potato bed. Season with salt and pepper, add the lemon zest, dill, and the rest of the butter. Spoon 15g wine over each.

  5. Fold the parchment over the fish and crimp the open edge in small overlapping folds, tucking the last fold under. Seal it fully but don’t wrap it tight — the packet needs room to inflate.

  6. Bake on the hot sheet for 15 minutes for fillets 2.5cm thick, until the packets have puffed and the salmon reads 125°F at the thickest part. Rest 4 minutes sealed.

  7. Cut each packet open at the table. Pour the juices over the fish.

Notes

  • The blanch is the step that decides this. 3mm slices don’t cook through in 15 minutes of trapped steam, and it’s the one failure nothing can fix once the packet is sealed. Raw potato works only sliced mandoline-thin, and then it needs 20–25 minutes — long enough to overcook the fish.
  • 15g of wine per packet, no more. The fish releases its own moisture and the paper holds all of it. Add more liquid and it poaches grey instead of steaming.
  • The packet should inflate. Flat means the seal leaked and the steam left. Crimp in small overlapping folds and tuck the last one under — sealed fully, but not wrapped tight, since the steam needs room to expand.
  • Skin off. In a sealed packet it never crisps, it goes slack. Skin-on is fine if the fish sits skin-down on the potatoes, but it buys nothing here.
  • Zest, not lemon slices. Slices sitting on the fish through 15 minutes of steam turn the pith bitter. Most published versions use slices anyway.
  • Pull at 125°F at the thickest part; it climbs a few degrees resting sealed. 125–130°F is medium, 145°F is the FDA seafood floor.
  • Time scales with thickness, not weight. 15 minutes suits 2.5cm. Under 2cm, check at 10; over 3cm, allow 18–20.
  • Foil works, and is what the French home versions use, but it reacts with wine and lemon. Using foil, swap the wine for water.
  • Sliced fennel or thin asparagus on top of the fish, or olives and thyme in with the potatoes. Anything wetter breaks the liquid budget.
  • Assemble up to 4 hours ahead and refrigerate. Bake from cold, adding 2 minutes.