Slow Roasted Tomato Sauce

Tomatoes are cut in half and placed cut-side down on a baking sheet to slow-roast them.
Tomatoes are cut in half and placed cut-side down on a baking sheet to roast them.

Thick, rich slow-roasted tomato sauce is super-easy to make. Last year I gave directions in a blog post. Now that my tomatoes are getting ripe in the garden, I think it’s time to re-post. It will save you a lot of effort and mess. No peeling or chopping required!

Since fresh tomatoes contain a lot of liquid, homemade sauces usually require hours of stovetop simmering to thicken. But if you roast them in the oven at a low, slow temperature —  around 200-225 degrees — it removes most of moisture. Several pounds of tomatoes can be condensed and blended into several cups of sauce that be used immediately, or frozen for later.

Roasting caramelizes the tomatoes’ natural sugar, giving them a deep, rich sweetness.

You don’t have to do any peeling. You just cut the tomatoes and place them cut-side down on a cookie sheet to roast. After you take them out of the oven,  just pinch the skins and they slip right off. Then puree the tomatoes and use the sauce as you would any tomato sauce or paste.

The only drawback to slow-roasting is that it ties up your oven for a long period of time — about six to eight hours. And, it adds some heat to your kitchen, although the temperature is low.

Because of this, I often let my tomatoes roast during the night, and wake up thinking I’m in an Italian restaurant.

I like to use the sauce in my spaghetti sauce and Garden Tomato Bisque.


Garden Tomato Bisque

And since the sauce is condensed, you can freeze it in small containers for future use. I’d rather do that than home-can tomatoes. USDA guidelines state that quart jars of tomato products should be processed in a boiling water bath for 95 minutes, for Wasatch Front altitudes.  That’s a lot of hot water sloshing around on your stove and steaming up your kitchen.

Don’t get impatient and turn up the heat. I tried roasting a batch of tomatoes at 350 degrees. After an hour, the skins were charred and the tomatoes had a burnt flavor. The kitchen also reeked.

The following recipe uses plum tomatoes. The round, slicing-style tomatoes are usually larger and more watery, so add a little more roasting time. If your plum (or roma) tomatoes are small, use lower heat or less roasting time.


About 20-25 medium or large plum tomatoes

1 tablespoon olive oil

Italian seasoning (dried basil, rosemary, oregano), optional

About 1/2 teaspoon salt

1. Spread the olive oil on a large baking sheet or pizza stone. Sprinkle it with the herbs, if using, and salt. You can also use a silicone baking mat (Silpat).

2. Cut off the stems of the tomatoes and cut each tomato in half lengthwise.

3. Place the tomatoes cut-side down on the pan. It’s OK if they touch; they will shrink during cooking.

4. Turn the oven to 200 degrees. Place the tomatoes in the oven and let them roast for 6-8 hours.

5. Check occasionally to make sure they’re not burning. You can turn down the temperature as low as 170 if you need to let the tomatoes roast longer.

6. The tomatoes should look shriveled and dark red, but still pliable. Turn off the oven and let them cool for a half hour or more.

Pinch the skins; they should lift off.  Place the tomatoes in a blender or food processor and puree. You can leave the sauce a little chunky if desired.

You may want to strain the sauce through a sieve to remove seeds, but I think the seeds are the proud badge of a homemade sauce.

This recipe makes about 2 to 3 cups of very thick tomato sauce, but not quite as thick as tomato paste. You can freeze it, or use it immediately on pasta, pizza and any other way that you would use tomato sauce.

Click here for my Garden Tomato Bisque recipe.

Here are two other bloggers that have featured Slow-Roasted Tomatoes.

Kalyn’s Kitchen 

Apron Strings


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