Sterilize a quart jar and set aside. Combine the salt, oil, lemon juice, mustard and celery seeds, and the garlic and set aside. Place about 15 shrimp in the jar, then put a layer of about 4 bay leaves. Put a layer of onion slices, then continue making similar layers until the jar is filled and all of the ingredients are used. You will have to pack the jar fairly tightly to get them to fit. You may have to push down on the ingredients a little. (I use a tall, narrow olive or capers jar.)

When the jar is full, stir the oil mixture well and pour slowly into the jar. Use a fork or a spatula to run down the sides to release air bubbles and to make sure the jar fills. If well packed, the jar will hold all of the ingredients perfectly.

Put the lid on the jar and turn it over to make sure everything is coated with oil and that the air bubbles are out. Right the jar, open it again, and push the ingredients down again so that they are covered with a film of oil.

Refrigerate for at least 24 hours before serving. When you remove shrimp from the jar, be sure to use a clean fork, never a finger. Before returning the jar to the refrigerator, make sure the remaining ingredients are covered with a film of oil and they will last easily for 2 weeks.