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1
Drain the tuna: save the oil from homemade tonno; discard the oil from canned tuna.
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2
Trim the scallions and remove all loose or wilted layers, keeping all the tight and tender white and green; dont cut them.
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3
Rinse the tomatoes and make a slit in the skin at the stem end of each.
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4
Bring 2 quarts of water to the boil in a saucepan; set up a bowl of icy water nearby.
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5
Drop in the tomatoes and blanch for about 1/2 minute; scoop them from the pot and drop into the ice water.
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6
Now blanch the scallions in the boiling water for 2 to 3 minutes, just to soften them, then refresh in the ice water.
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7
Drain the chilled tomatoes; peel off and discard the skin.
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8
Lift out the chilled scallions, pat dry with paper towels, and slice crosswise into 1-inch lengths.
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9
Peel the onion, trim the ends, and slice lengthwise in quarters; cut the wedges crosswise in half.
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10
If using a big onion, slice up a heaping cup of 1-inch wedge-shaped pieces.
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11
Put the onion pieces and the 2 tablespoons of olive oil in a medium skillet set over medium-high heat.
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12
Sprinkle on 1/4 teaspoon salt, and cook, toss, and stir for 1 to 2 minutes, to get all the onion pieces sizzling and softening, then pour in the white balsamic vinegar.
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13
Toss the onion in the vinegar for a minute or so, then transfer to a mixing bowl.
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14
When the onions have cooled a bit, break apart the drained tuna into 1-inch chunks and drop them in the bowl with the scallions and the capers.
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15
Toss together, then sprinkle the dressing ingredients over them and toss some more.
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16
Drop the peeled tomatoes into the bowl, and fold them into the salad so theyre coated with dressing but dont break apart.
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17
Let the salad marinate for an hour or so.
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18
Adjust the seasonings and dressings to taste, and serve on a big platter or individual plates.
