This article is from the Food Preserving FAQ, by Eric Decker firstname.lastname@example.org with numerous contributions by others.
>From Brenda Sharpe :
This is my most requested preserve recipe, for a sweet green "ketchup"
that goes well with beef and cheese. The original recipe came from a
congregation of nuns in Montreal, Quebec, Canada. Full recipe makes
approximately 12 500 mL (pint) jars. The recipe can be halved.
30 green tomatoes (the size of small apples), sliced (with skins
on but cut off stem and blossom ends and any nasty bits)
6 onions, peeled and sliced or chopped
1/2 cup pickling (coarse, non-iodized) salt
Slice tomatoes and onions (a food processor is great for this) and
layer in a non-reactive, large pot with salt. Let stand overnight. In
the morning, drain well. Add: 16 apples (hard and sour), peeled and
sliced 4 cups granulated sugar 1/4 cup pickling spices, tied up in a
cheesecloth bag (leave a long string on for taking out later!) White
Vinegar (must be at least 5% acidic) Add vinegar until three-quarters
(3/4) of ingredients are covered (DO NOT COVER COMPLETELY). Bring to a
boil and then reduce to a simmer; simmer 1 to 1 1/2 hours until apples
are transparent and everything is well cooked and fragrant. Remove
spice bag. Pour into sterilized pint jars leaving 1/4 inch head space.
Seal and process in a boiling water bath canner 10 minutes. This is
great on burgers or eggs; one friend likes it on cheese sandwiches;
another eats it like a dessert!