This is a delicious simple sauce that can be served with your favorite fresh pasta. WASH THE TOMATOES WELL; then cut them into sixths or, if they are large, into eighths. Warm the olive oil in a large, flat stainless-steel or non-stick pan; add the tomatoes, onion, salt to taste and rosemary. Cook over gentle heat until the skins are wrinkled and have really cooked away from the flesh, about 30 minutes. The tomatoes should be melting into a puree. Pass them through a food mill. Check the consistency; if you wish a thicker sauce, return it to the pan and cook over medium-low heat until it is the thickness you like. Add salt to taste and process in jars, according to canning directions, or freeze. Makes 1 Quart