Simmer chicken with onion, celery tops, 1 teaspoon of the salt, peppercorns and water in a large saucepan 30 minutes, or until tender.
Remove chicken from broth; cool until easy to handle.
Strain broth into a 2 cup measure; add water, if needed, to make 2 cups; set aside for making the sauce in Step 3.
Remove skin from chickens, then pull chicken from bones; dice meat. (There should be about 4 cups.)
Melt butter or margarine in a large saucepan; blend in flour, remaining 1 teaspoon salt, nutmeg and pepper; cook, stirring constantly, just until bubbly.
Stir in the 2 cups chicken broth; continue cooking and stirring until sauce thickens and boils 1 minute. (It will be very thick.)
Remove from heat.
Stir in lemon juice, diced chicken, pimientos and water chestnuts.
Spoon half of mixture into a 6 cup freezer container then cool, cover, label, date and freeze.
Stir cream very slowly into remaining mixture in saucepan.
Heat, stirring often, just until hot. (If you prefer mixture thinner, stir in about 1/2 cup milk.)
Spoon into patty shells, or over your choice of buttered toast, rice or mashed potato.