In a shallow bowl, stir together the flour, and salt.
Whisk in the egg, tablespoon amd a half of oil,milk, and water until batter is smooth. The batter should be thick enough to stick to the apples, and coat them. If the batter is to thin, add more flour. If batter does not stick, toss the apples with a bit of flour.
Add and Heat 1/2 inch vegetable oil in a deep heavy skillet to 375 degrees.(This would be the 2 cups ).
Coat apple slices with batter, and place 4 or 5 slices into hot oil at a time.
Fry until golden on one side, and then use tongs to flip and fry until brown on other side.