Beat the eggs, sugar, and salt together in a mixing bowl. Whisk in the milk, followed by the flour; whisk until smooth.
Heat oil in a deep-fryer or large saucepan to 375 degrees F (190 degrees C).
Soak the bread slices in the egg mixture until the egg has penetrated through to the center of the bread. Wipe off the excess egg. Cook in the deep-fryer several pieces at a time to avoid overcrowding. Cook until golden brown on both sides and no longer soggy in the center, about 4 minutes. Drain the French toast on a paper towel-lined plate before serving.