Tuna and onion sandwich

Ingredients

• 2tartarughe rolls
• 80 gpitted black olives
• 100 gpitted green olives
• 50 gsalted capers, desalinated
• 30 glamb’s lettuce
• 150 gred onions
• 2 tablespoons (30 ml)extra-virgin olive oil
• to tastefine salt
• 15 gbrown sugar
• 150 gwater
• 200 gtuna, previously deep-frozen
• 1 tablespoon (15 ml)extra-virgin olive oil
• to tastefine salt
• zest of 1 lemonlemon zest
• 1egg yolk
• juice of ½ lemonlemon juice
• 125 gsunflower oil
• to tastefine salt
• to tasteblack pepper

Instructions

1. 1

   Make the mayonnaise

   Use fish that has been properly deep-frozen beforehand. Put the egg yolk and the juice of half a lemon in a bowl. Whisk with an electric whisk, gradually drizzling in the sunflower oil without stopping. Continue until all the oil is incorporated and the mayonnaise is firm.

2. 2

   Season and chill

   Add salt and pepper, stir with a spatula and put the mayonnaise in the fridge. Peel the onions and cut them into wedges.

3. 3

   Start the onions

   Heat the olive oil in a small pan. Add the onions, salt and brown sugar.

4. 4

   Stew the onions

   Pour in some of the water; the amount needed depends on the size of the pan, and you can add more if necessary. Stew the onions for 10 minutes in total. Meanwhile, cut the previously deep-frozen tuna into small cubes.

5. 5

   Season the tuna

   Season the tuna with salt, olive oil and the zest of one lemon. Mix well and keep it in the fridge. After about 10 minutes, the onions should be soft and glossy; turn off the heat and set them aside.

6. 6

   Chop the olives

   Put both types of olives and the desalinated capers on a chopping board. Chop them with a knife until finely minced. To assemble, cut both rolls in half.

7. 7

   Layer the filling

   Spread mayonnaise on the bottom half of each roll, then add the tuna and the chopped olive-and-caper mixture.

8. 8

   Finish the sandwiches

   Top with the onions and lamb’s lettuce, close the sandwiches and serve.

What is a tuna and onion sandwich?

This is an Italian-style filled roll, bringing together tuna, onions, olives, capers and salad leaves. The recipe’s tartarughe rolls provide a crusty, substantial base for the contrasting fillings.

The method combines gently stewed onions with tuna served raw, so the result is both sweet and savoury, with briny, citrusy notes. Homemade mayonnaise ties the layers together.

Nutrition and macros by portion

The nutrition label shows one serving as written: 1300 calories, 38g protein, 72g carbs, 96g fat.

The rolls and brown sugar provide most of the carbohydrates, while the sunflower and olive oils, mayonnaise and olives contribute much of the fat. Tuna supplies most of the protein. Balance the sandwich with extra salad or vegetables on the side, and use a smaller amount of the olive-and-caper mixture if you prefer a less salty plate.

Choosing the tuna

Food safety: use tuna that has been deep-frozen beforehand, as specified in the recipe. Keep it chilled while preparing the other components and until you assemble the rolls.

Cut the tuna into small, even cubes so it is easy to eat in the sandwich. Lemon zest, olive oil and salt season it without masking its flavour.

Getting the onions tender

Slow cooking: the onions are stewed with olive oil, salt, brown sugar and water for 10 minutes. Add the water in stages, as the quantity needed can depend on the pan.

Doneness cue: look for onions that are soft and glossy before taking the pan off the heat. Avoid letting the pan dry out while they cook; add more water if needed.

Making the mayonnaise

Steady whisking: begin with the egg yolk and lemon juice, then pour in the sunflower oil gradually while whisking continuously. A slow, steady stream helps the mixture become firm.

Keep the finished mayonnaise refrigerated until you are ready to assemble the sandwiches. Because it contains raw egg, use fresh, properly handled ingredients and avoid leaving it at room temperature.

Balancing the salty filling

Olives and capers: chop the black and green olives together with the desalinated capers to make a savoury relish. Taste before adding extra salt elsewhere, since these ingredients already bring plenty of saltiness.

Lamb’s lettuce: add it at the end, just before closing the rolls, so it stays fresh and gives the filling a lighter contrast.

Assembling and serving

Layering: spread mayonnaise on the lower half of each roll, then add the tuna, olive-and-caper mixture, onions and lamb’s lettuce. This order keeps the wetter ingredients supported by the bread.

Serve as soon as the sandwiches are assembled, while the rolls still have their texture. They make a filling lunch on their own or alongside a simple green salad.

Recipe notes & tips

• Use tuna that has been deep-frozen beforehand, as the recipe specifies.
• Keep the tuna and mayonnaise chilled while you prepare the onions and olive mixture.
• Pour the sunflower oil into the egg yolk gradually while the electric whisk keeps running.
• Add the onion water in stages and top it up if the pan starts to dry out.
• Chop the olives and capers finely so their flavour is spread through each bite.
• Assemble the rolls shortly before serving to keep the lamb’s lettuce fresh.

Variations

• Add herbs: mix chopped parsley into the olive-and-caper relish for a fresh note.
• Use a different roll: choose another crusty bread roll if tartarughe rolls are unavailable.
• Adjust the brine: use fewer capers for a milder, less salty filling.
• Add extra greens: increase the lamb’s lettuce for more fresh crunch.
• Make it sharper: add a little more lemon zest to the tuna before chilling.

Common mistakes to avoid

• Using tuna that has not been deep-frozen: follow the recipe’s instruction and use tuna that has been properly deep-frozen beforehand.
• Adding all the mayonnaise oil at once: drizzle it in gradually while whisking continuously.
• Letting the onions dry out: add more water if needed as they stew.
• Over-salting the filling: remember the olives and capers are already salty, and season sparingly.
• Assembling too early: add the lamb’s lettuce and close the rolls close to serving time.

How to store

Keep the tuna, mayonnaise and cooked onions covered and refrigerated, and assemble the rolls just before eating. For food safety, use the raw tuna and egg mayonnaise promptly rather than storing assembled sandwiches; discard anything that has been left at room temperature for an extended period.

Frequently asked questions