- '2 pounds zucchini (preferably small; 6 to 8)'
- '2 pounds boiling potatoes'
- '1 1/2 cups olive oil'
- '2 1/2 cups chopped Spanish onion (1 pound)'
- '10 large eggs'
- 'a 12-inch nonstick skillet'
- Coarsely grate zucchini, then toss with 2 teaspoons salt and let stand 30 minutes
- While zucchini stands, peel potatoes and cut into 1/3-inch dice
- Heat oil in skillet over medium-high heat until hot, then add potatoes, onion, and 3/4 teaspoon salt
- Reduce heat to medium-low and cook (without browning), uncovered, stirring occasionally, 30 minutes
- Transfer zucchini to a colander to drain, then squeeze small handfuls to remove as much liquid as possible, transferring as squeezed to a small bowl
- Add zucchini to potatoes and cook, stirring occasionally, until potatoes are tender and zucchini is slightly browned, about 15 minutes
- Drain vegetables in colander set over a bowl, reserving oil
- Cool 5 minutes
- Lightly beat eggs in a large bowl, then stir in vegetables, 1 tablespoon reserved oil, 3/4 teaspoon salt, and 1/2 teaspoon pepper
- Return 1 tablespoon reserved oil to skillet and add egg mixture, pressing potatoes flush with eggs
- Cook over low heat, covered, until almost set and underside is golden, 12 to 15 minutes
- Remove from heat and let stand, covered, 15 minutes
- Run a rubber spatula around tortilla and shake skillet gently to loosen (if bottom sticks, carefully slide spatula underneath)
- Slide tortilla onto a large flat plate, then cover with skillet and invert tortilla back into skillet
- Round edge of tortilla with rubber spatula and cook over low heat, uncovered, until set, about 15 minutes more
- Slide tortilla onto a serving plate and cut into wedges
- Serve warm or at room temperature
