For the batter, whisk egg, flour and water until smooth. Cover and leave to swell in the refrigerator for 30 minutes.
Remove the skin from the apples, remove the core with a corer and cut the fruit diagonally into centimeter-thick slices.
Heat the oil for frying. Pull each apple slice through the batter, then fry in the hot oil until pale golden. Drain well on kitchen roll.
In the meantime, boil the sugar with vinegar and water in a small pot to a golden syrup. It has reached the right consistency when a drop of it quickly falls to the bottom in ice-cold water.
Dip each of the baked apple pieces into it and place them end to end on an oiled platter. Baste with cold water to set the sugar. Quickly bring to the table while the apple pieces are still warm at the core.
Flavor frying fat with a little sesame oil.