Pick over and wash peas. Put peas in to soak overnight. Cook them in the same water. Bring to boil, add sliced onions. Simmer for 3 hours or until the Peas are soft. Run them through a strainer. Add the soup stock. Diced celery, potatoes, carrots and parsnips may be added and cooked with the soup the last quarter hour. Ad salt last. To make a thicker soup cook 6-7 potatoes, press with the peas thru the strainer.