Remove any bruised outer leaves of a large head of endive and discard.
Wash the inner leaves and lay on paper towels. Tear the leaves by hand into a small bowl with or without the ribs.
Squeeze some lemon juice over the leaves and use a wooden spoon to toss to coat.
Using a sharp kitchen knife, thinly slice the celery ribs and leaves on a severe angle.
Add to a large salad bowl (separate from the leaves) then slice the apple into thin slices as well.