Roasting gives tomatoes, and the subsequent sauce, a richer flavor than you get from just cooking them in a pot. You don't have to limit your use of the roasted tomatoes to making sauce, of course - if you skip the simmering down step you can turn them into a delicious soup. Or just chop the tomatoes and use them straight - with pasta, on pizza, etc.
7 1/2 lbs paste tomatoes (such as Roma, San Marzano, Amish Paste, etc)
6 cloves garlic, minced
1 shallot, minced
Salt and pepper to taste
Other seasonings as desired: fresh or dried basil, oregano, thyme, sage, parsley...your choice
Preheat the oven to 400 degrees.
Core the tomatoes and spread them out in a single layer in a large baking dish (or two); use a dish with reasonably high sides, as the tomatoes will give off a good bit of liquid. Put them in the oven and roast for 30-40 minutes, stirring once or twice. When they're done they will be very soft and the skins will probably have split. Remove from the oven and scoop the tomatoes into a colander in the sink to drain.
You can stop here and use the tomatoes as you like. Or proceed:
When the tomatoes are cool enough to work with and have drained off some of their excess liquid, put them through a mill (I used my Squeezo Strainer, which is awesome for tomato sauce and apple sauce; if you want to get one, check eBay - I got a lightly used one for half the retail price that way). After this step I had about 8 cups. You can stop here and make tomato soup. Or proceed:
Pour the milled tomatoes into a Dutch oven or other large, heavy-bottomed pot. Simmer over low heat until the sauce reduces to a consistency you like. In the meantime, heat a little olive oil in a small skillet and saute the garlic and shallot, then add them to the sauce. When the sauce is done reducing, add salt and pepper to taste. I ended up with about 4 1/2 cups; precise yield will depend on how much you reduce the sauce.
Feel free to add additional seasonings to the sauce. It is remarkably good with just the garlic and shallot, but any of the herbs listed above (or a combination) would be nice additions.
Yield: 4-5 cups of sauce.