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1
Peel potatoes and cut into 1/3-inch dice (2 1/4 cups).
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2
Heat oil in a 10-inch nonstick skillet over moderate heat until hot but not smoking, then reduce heat to moderately low and cook potatoes, onion, and 1 teaspoon salt, stirring occasionally, until potatoes are tender, about 20 minutes.
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3
Cook kale in a 4- to 6-quart pot of boiling salted water until wilted, 2 to 3 minutes.
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4
Drain in a colander and immediately transfer to a bowl of cold water to stop cooking.
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5
Drain again, squeezing handfuls of kale to extract excess moisture, then coarsely chop.
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6
Add kale to potato mixture and cook, stirring occasionally, until kale is tender, about 5 minutes.
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7
Drain vegetables in colander set over a bowl, reserving drained oil, and cool 10 minutes.
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8
Lightly beat eggs in a large bowl, then stir in vegetables, 1 tablespoon drained oil, and remaining 1/2 teaspoon salt.
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9
Add 1 tablespoon drained oil to skillet, then add egg mixture and cook over low heat, covered, until sides are set but center is still loose, about 12 minutes.
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10
Remove from heat and let stand, covered, 15 minutes.
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11
Shake skillet gently to make sure tortilla is not sticking (if it is sticking, loosen with a heatproof plastic spatula).
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12
Slide tortilla onto a large flat plate, then invert skillet over tortilla and flip it back into skillet.
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13
Round off edge of tortilla with plastic spatula and cook over low heat, covered, 10 minutes more.
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14
Slide tortilla onto a plate and serve warm, cut into wedges.
