Prepare Tomato Aspic and pour a thin layer into a small mold which has been rinsed in cold water.
Refrigerate until firm; keep remaining Aspic at room temperature.
Gently open the petals of the artichoke hearts and press them lightly apart.
Mash 1/3 cup of the cottage cheese and use to fill artichoke hearts.
Put the hearts, cheese side down, into the mold containing the layer of aspic.
Add a layer of diced celery, sprinkle with onion salt, and fill mold with remaining Aspic (it should be partly set but not firm).
Place mold back into the refrigerator until firm.
Unmold on bed of lettuce.
Serve topped with remaining 1/3 cup of cottage cheese mashed with a tablespoon or so of water.