Trout al Cartoccio, Baked in Parchment

Why this recipe works for weight loss

Trout sits in the gap between cod and salmon, and that gap is the whole point. Per 100 g raw: cod is 82 calories with 17.8 g of protein, trout 141 with 19.9 g, salmon 208 with 20.4 g. Expressed as protein per 100 calories that is 21.7 for cod, 14.1 for trout, 9.8 for salmon. Cod wins the arithmetic outright and our baked cod with chickpeas and tomatoes is that version written out in full — but cod is a fish that needs help, and a packet is a gentle place. Trout has enough fat of its own (6.2 g per 100 g) to come out of fifteen minutes of steam tasting like something rather than like a diet. One fillet puts 27.9 g of protein on the plate, which clears on its own the 20 g floor every main in this collection is built to; protein is also the macronutrient with the best evidence behind it for holding appetite down and protecting lean mass while calories are restricted (Leidy et al., 2015).

The potatoes are in here on purpose, and the reason is satiety rather than tradition. Potatoes have a worse reputation in American kitchens than they deserve: in the classic satiety-index work, boiled potatoes scored higher than any other food tested — more than three times white bread, gram for gram of calories (Holt et al., 1995). Plain boiled potato is bulky, watery and filling, and at 77 calories per 100 g it buys a lot of volume cheaply. Six ounces a person is 131 calories, 30 g of carbohydrate and 3.7 g of fiber, and it is what makes this feel like dinner instead of a fillet on a plate. Leave the skins on — most of that fiber is in them.

Fifteen minutes of steam, and no added fat to carry the heat. The packet is a sealed steam oven: the liquid is a tablespoon of wine per person plus whatever the leeks and potatoes give up, and the trapped vapor cooks the fish from every side at once at a temperature that cannot run away from you. This matters to the numbers more than it sounds. The total fat on the plate is 16 g, of which 8.7 g is the trout's own and 6.8 g the olive oil; saturated fat is 2.9 g. Pan-searing the same fillet would add a teaspoon of oil per person before anything else happened, and roasting the potatoes properly would add a tablespoon. For comparison, our pan-seared salmon with salmoriglio is 497 calories with 32 g of fat — the same protein, twice the fat, and a sauce worth it.

Freshwater trout is on the short list of fish you can eat often. The Dietary Guidelines for Americans 2020–2025 ask adults for at least 8 oz of seafood a week and most Americans manage about half of that; one serving here is 5 oz, so two dinners covers it. Trout is in the "Best Choices" group of the FDA and EPA's Advice About Eating Fish — the lowest-mercury category, safe at two to three servings a week including in pregnancy — and the American Heart Association's seafood advisory asks for one to two fish meals a week specifically for the long-chain omega-3 fats that oily and semi-oily fish carry (Rimm et al., 2018). This site's nutrition table has no omega-3 column, so you will not find a milligram figure here: the claim is the fish, not a number we cannot calculate.

Where the 586 mg of sodium comes from, item by item. 388 mg is the 3/4 teaspoon of kosher salt, divided between four fillets and their beds. 100 mg is the capers — 2 tablespoons for the whole recipe, and they are salty enough that the dish would taste thin without them and over-salted with twice as many. 71 mg is the trout itself, and the potatoes and leeks bring 24 mg between them. Nothing here is cured, canned in brine or jarred except those capers, which is why a plate this savory lands at a quarter of the daily ceiling rather than half of it.

Tips from our kitchen

• Buy the fillets boned and butterflied, and accept that the skin will be soft. American fish counters sell farmed rainbow trout as a butterflied whole fish — two fillets joined along the back — for about half the price of salmon; cut it down the middle and you have two portions. Run a fingertip across the thick end for pin bones before you build the packets. One thing to be clear about: this is not a crisp-skin dish. Fifteen minutes of steam leaves trout skin tender and pale, and it is perfectly good eating, but if you want crackle you want a pan, not paper.
• Waxy potatoes, and 1/8 inch is not a suggestion. Yukon Gold, red-skinned, fingerlings — anything waxy holds its slices through a boil and a bake. Russets fall into mash in the packet and make the bottom watery. Thickness is the one measurement in this recipe worth being fussy about: 1/8 inch (3 mm) boils to bendable in 7 minutes and finishes in the oven in 15, and a slice twice that thick will not, no matter how long you boil it.
• Parchment over foil, for a reason you can taste. There is a quarter cup of wine and two tablespoons of lemon juice in here, and acid sitting against aluminum for fifteen minutes at 425 °F can pick up a faint metallic edge. Foil is easier to seal and I use it when the parchment runs out — but if you have both, use the paper. What you cannot use is wax paper, which melts, or a loose tent of either material, which is just roasting with extra steps.
• Assemble ahead, bake from cold. The packets can be built, sealed and refrigerated up to 6 hours, which makes this the easiest dinner party main in the collection: four parcels on a sheet pan, one oven, no pan to scrub. Add 2 minutes to the bake if they go in fridge-cold. Do not build them the night before — the salt and lemon start curing the fish and the texture goes firm and faintly hammy.
• If you want a sauce, do not make one. The liquid in the bottom of each packet is already a sauce: wine, lemon, olive oil and the juices of the fish and the vegetables, emulsified by fifteen minutes of agitation in a sealed bag. Tip the packet and spoon it back over the fillet. Adding butter or cream at the table is not wrong, it is just a different recipe, and it costs about 100 calories a tablespoon.
• Scaling down to one or two. Everything divides cleanly: one fillet, 6 oz of potatoes, half a leek, 1 1/2 teaspoons of oil, a tablespoon of wine. The only thing that does not scale is the oven, so a single packet is a slightly extravagant way to heat a kitchen — two is the efficient minimum.

Variations

• With cod, for the lean version: 367 calories and 30 g of protein. Same packet, same bed, same 15 minutes, 8.2 g of fat instead of 16. Cod is the better arithmetic by a distance and a packet is the right place for it, because the one thing cod does badly is dry out. Cut the fillets to 5 oz pieces of even thickness; thick loin pieces want 18 minutes. If you would rather have the lean fish written out properly than swapped in, that is baked cod with chickpeas, tomatoes and olives.
• With salmon, right at the ceiling: 544 calories and 33 g of protein. A 5 oz salmon fillet pushes the packet to 26 g of fat and 544 calories — six calories under the 550 line this collection is built to, which is either reassuring or alarming depending on how you read it. It is an excellent packet and the skin-side-down trick matters more, since salmon skin left face up in steam is unpleasant. Worth knowing: the same fish seared in a pan with a lemon-oregano sauce is 497 calories, because the fennel-and-orange salad underneath weighs less than potatoes do.
• Without the potatoes: 319 calories, 12 g of carbohydrate. Drop them, double the leeks, and add a halved fennel bulb sliced thin — the packet becomes a light main for someone eating low-carbohydrate, and it loses the 7-minute boil along with them, which makes it a 30-minute recipe. The cost is specific and worth stating: fiber falls from 5.5 g to 1.7 g and the plate no longer eats like a full dinner. Add bread and you have given the calories back.
• For a bigger appetite: 2 1/2 lb of potatoes, 531 calories and 60 g of carbohydrate. The same four packets with 10 oz of potatoes each instead of 6, which is how an Italian household would actually portion this for someone who had been outdoors all day — 35 g of protein, 7.8 g of fiber. Be clear about what it is and is not: 60 g of carbohydrate is a good dinner, not a carb-load. The 80-to-120 g pre-race range lives in the endurance recipes and the carb-loading guide, and for potatoes and seafood in one dish at that scale the right answer is tiella barese.
• In summer, cherry tomatoes and zucchini instead of leeks. Halve a pint of cherry tomatoes, slice a zucchini into coins, keep the potatoes and the capers, and skip the wine — the tomatoes bring their own liquid. It is the Mediterranean version of the same packet and it is what you will want in July. We have not run the numbers on it, so the table above does not apply.

Storage & meal prep

A baked packet does not keep as a packet — the paper goes limp and the potatoes keep drinking the juices — so lift the contents into a container as soon as it is cool enough to handle. It keeps 2 days in the fridge and is genuinely good cold, the fish flaked over the potatoes with an extra squeeze of lemon, which is the way I prefer the leftovers to the reheated version. If you want it warm, a 300 °F oven for 8 to 10 minutes in a covered dish with a spoonful of water is the only method that does not toughen the trout; a microwave on full power drives the fat out of the fish and gives the kitchen the smell the packet was there to prevent. Do not freeze it, cooked: the potatoes go grainy and trout freezes badly twice. The two things that do keep ahead are the components — boiled potato slices hold 24 hours in the fridge spread on a plate under a damp towel, and washed leeks hold 2 days in a sealed bag — which turns this into a ten-minute assembly on the night.