Grate 1 pound zucchini, scrubbed and trimmed, and spread it in a large colander. Sprinkle the zucchini with 2 teaspoons salt, toss it, and let it drain for 30 minutes. Transfer the zucchini to a tea towel and squeeze out the remaining liquid.
In a bowl combine the zucchini, 1 egg, lightly beaten, 2 teaspoons minced onion, and 1/4 teaspoon each of salt and white pepper, or to taste, add 2 or 3 tablespoons stale bread crumbs, or enough to absorb all the liquid, and stir the mixture until it is well blended. Heat enough vegetable oil in a skillet to measure 1/4 inch over moderate heat until it is hot (375 degrees F.). Divide the zucchini mixture into 4 balls. Transfer 2 balls to the pan, flatten them with a spatula to form 1-inch-think rounds, and cook them for 2 minutes on each side, or until they are golden. Transfer the rounds with a slotted spatula to paper towels to drain. Flatten and cook the remaining balls in the same manner. Arrange the rounds on a heated serving dish and top each round with a dollop of sour cream or plain yogurt.