Heat oil in a deep-fryer or large saucepan to 375 degrees F (190 degrees C).
Toss cauliflower florets with salt in a bowl.
Whisk egg and vegetable oil together in a separate bowl. Whisk in flour and milk until batter is smooth.
Working in batches, drop cauliflower florets into batter; stir to coat.
Working in batches, gently lower battered cauliflower into preheated oil; fry until florets rise to the top and float, 2 to 4 minutes. Carefully turn pieces over and continue frying until golden brown, about 2 minutes more. Use a slotted spoon to transfer fried cauliflower to a paper towel-lined plate.