Combine flour and salt in a medium mixing bowl. Stir in cold water and egg yolks. Mix just to combine.
In another bowl, beat the egg whites just until frothy. Fold into batter mixture. Do not over mix. Batter should be a little lumpy. Cover and refrigerate for 30 minutes.
Heat 2″ to 3″ (5 cm to 7.5 cm) oil in deep-fryer or heavy, deep saucepan to 375ºF (190ºC). Working in batches, dip vegetables in batter. Fry 2 to 3 minutes, or until lightly golden brown, turning as needed for even brownness.
Drain on paper towels. Serve immediately or keep warm in 175ºF (80ºC) oven.