Using the large holes of a box grater, coarsely grate ginger. Place in a 6-inch square of cheesecloth and squeeze out juice into a bowl; discard ginger and reserve juice. Finely zest lemon, then squeeze enough juice to make 1 tablespoon plus 1 teaspoon.

In a large saucepan combine water, butter, 2 tablespoons sugar, lemon zest, 1 tablespoon lemon juice and pinch salt. Bring just to a boil, then remove from heat. Whisking, slowly add flour in a thin stream, then stir in ginger juice. Let cool, 10 minutes.

Using a fork, blend eggs 1 at a time into batter, then add remaining teaspoon lemon juice and citron.

Place remaining 2 teaspoons sugar in a large shallow bowl. Line a large plate with paper towels. Heat about 3 inches oil to 375° in a 4- to 5-quart heavy pot over medium-high heat. Drop half-tablespoonfuls batter into oil, about 8 at a time, and fry until puffed and golden, turning once, 1 to 1 1/2 minutes. Using a slotted spoon, transfer fritters to paper towels to drain; immediately roll in sugar. Serve warm.