In medium bowl, combine sugar, flour, and salt. Add melted butter, lime peel, and lime juice. Stir until blended. Set aside.
Separate eggs into 2 bowls, being careful not to get any yolk in the whites. Beat egg yolks, then add the milk, stirring with a wooden or plastic spoon; stir into lime mixture.
In glass or china bowl (not plastic), beat egg whites until stiff. Fold gently into lime mixture. Pour batter into greased 8x8x2-inch baking pan.
Pour hot water into a large, shallow baking pan to 1-inch depth. Set pan of pudding batter into the hot water.
Bake in 350 degree F oven 40 minutes or until lightly browned. Serve warm or chilled, topping with whipped cream or softened vanilla ice cream.
