This section is from the book "Simple Italian Cookery", by Antonia Isola. Also available from Amazon: Simple Italian Cookery.
Take one-half of an old onion and chop it up fine. Take one small carrot, wash it, scrape it, and cut it into transverse slices; do the same with a stalk of celery, some parsley, and one fresh or canned mushroom. Then take a slice of ham (raw if possible), fat and lean, about four fingers wide and one finger high. Chop it up fine, and put it into a medium-sized saucepan with one tablespoon of butter. When the ham is colored, put in the chopped-up vegetables, one clove, salt, and pepper, and stir constantly, allowing the vegetables to cook thoroughly but not to burn, which will destroy the taste of the sauce. It should be a golden color. A little red wine may be added if you have it, but this is not necessary. Then add four fresh tomatoes, cut into several pieces, the skins removed, and the seeds taken out. Allow these to cook in the sauce until they sputter, then add a little water (or bouillon if you have it), allow it to boil for a few moments more, then take it off the fire and pass it through a sieve or fine colander, pressing hard so that all will pass through. If it is too thick after straining, add water or bouillon, and put it back and allow it to boil again a few moments. This sauce can be used for macaroni, gnocchi, left-over meat, egg, etc. The success of the sauce depends upon the proper frying of the onion in it.