In a large bowl, combine flour, cornstarch, baking powder and salt. Make a well in the center. All at once, add the water, egg yolk and pickle juice. Whisk to make a smooth batter. Cover and refrigerate for 30 minutes.

In a deep fryer or large saucepan, heat at least two inches of oil to 375°. In batches, dip pickle slices into batter, lightly and evenly coating them. Without crowding, place coated slices in the hot oil. Fry until golden and crisp, 1½ to 2 minutes.

Drain on paper towels and serve immediately.