Get Ready

• To make a thick tomato sauce or paste, start with roma-type tomatoes. These tomatoes are oval rather than round and typically smaller than slicing tomatoes. They have dry, meaty flesh that isn't particularly appetizing fresh, but cooks down into thick, hearty sauces. Drop the tomatoes in boiling water for a minute to loosen the skins. Peel the tomatoes, dice them and refrigerate them covered overnight in a bowl or pitcher. In the morning, drain off the liquid to ensure an even thicker sauce. You can also use canned tomatoes or crushed tomatoes. Drain the juice off canned tomatoes, but not crushed tomatoes, which is a thick tomato puree.

Low and Slow

• The secret to cooking tomatoes into a thick consistency is long, slow cooking over low heat. Cook the tomatoes in a heavy pot over low or medium-low heat, stirring occasionally. As the mixture cooks, moisture evaporates and the tomatoes become thick and pasty. On the stovetop, the process can take four to six hours. The sugars in tomatoes burn easily, so check them frequently and don't allow them to boil. You can also cook tomatoes in a slow cooker over low heat for eight to 10 hours. This method takes longer, but the tomatoes are less likely to burn.

Flavorings and Uses

• You can make a simple tomato paste with no seasonings to use in multiple ways or season the paste as you cook it. For a basic Italian sauce, add a bit of salt, sugar, garlic and basil near the end of cooking time. For a chunkier sauce, add sauteed onions and red peppers. These vegetables will break down during long slow cooking, just as the tomatoes do, to add flavor and sweetness. Pizza sauces are typically more robust. Add more garlic and basil, as well as Italian seasonings, such as marjoram, oregano and basil. Add this thick sauce to soups and stews or thin it and serve it over pasta.

Safe Storage

• Once the tomatoes have reached the desired consistency, allow the sauce to cool slightly. At this point, you can pack the sauce into covered containers and refrigerate it for up to one week. For longer storage, place the sauce in plastic freezer bags. Lay the bags flat in the freezer. Once the bags are frozen solid, you can stack them to conserve space. Use frozen bags of tomato sauce within three to six months. You can also can tomato sauce in pint or quart jars. Tomatoes are generally acidic enough to can using a water-bath canner, but if you add onions and peppers, which are alkaline, you must add an acidic ingredient, such as lemon juice or vinegar, or use a pressure canner. Follow a recipe specifically made for canning tomatoes to ensure safe results. Improperly canned tomato products can cause serious foodborne illness.