Caramelized Onion Tomato Jam

Jump to Recipe·Print Recipe· 5 from 2 reviews

This caramelized onion tomato jam is easy to make with only a handful of ingredients. It's a wonderful accompaniment to a cheese plate, charcuterie board, or even as a spread for sandwiches!

Caramelized Onion and Tomato Jam on Crostini

This post was originally published in 2018 and updated in 2021 with new photos and improved instructions.

This caramelized onion and tomato jam recipe is easy to make and so versatile. The secret ingredient is really just time! The onions are cooked low and slow, until they turn a nice deep brown color, becoming nice and sweet.

Then, balsamic vinegar is added to the pan, along with diced tomatoes and sugar. This is cooked down until the tomatoes break down a bit, turn a rich deep red color, and most of the liquid is evaporated.

The result is a thick, glossy jam that's sweet, tangy, and savory, all at the same time! This tomato jam tastes delicious on potato dishes, like my quick and easy recipe for home fries, grilled cheese, crackers, sandwiches, and pretty much anything else you can think of!

Recipe ingredients

Ingredient notes

Tomatoes: I used vine-ripened tomatoes, but you can use any type of similar tomato you have available, such as plum tomatoes. I haven't tried this with grape or cherry tomatoes however, so I can't say if using those would change the consistency of the jam at all.

Onion: I like using a sweet variety of onion, like Vidalia. I've also made this with red onion, which gives the tomato jam an even more beautiful, deep color. But, a white or yellow onion would also work.

Step by step photos

1. First, heat the oil in the pan and add the thinly-sliced onions and half the salt. Smooth the onions out evenly and allow to cook over low heat for 40 minutes or so until they reach a deep golden brown color. Remember to stir occasionally!

collage of onions before and after caramelizing in pan

2. While the onions are caramelizing, prep the tomatoes. Be sure to scoop the seeds out before chopping!

collage of tomatoes being seeded and chopped

3. Then, add the tomatoes, sugar, remaining salt, and balsamic vinegar to the caramelized onions. Turn the heat up a little bit and let the tomatoes simmer away, stirring occasionally. Eventually, most of the liquid will evaporate and the mixture will turn thick and jam-like!

collage of tomatoes before and after cooking in pan

Tips and tricks

I left the skin on my tomatoes and they didn't bother me a bit. The jam is chunky anyways so I thought the skins blended in with the texture just fine. But if you are an anti-skin person, feel free to skin your tomatoes first!
The sugar, vinegar, and salt in the recipe can all be adjusted to suit your own tastes. If you like more subtle flavors, feel free to add less sugar and salt from the beginning, and adjust toward the end of cooking, or even add a splash more vinegar toward the end of cooking to add more zip! The amount of sugar you need may also vary based on how sweet your tomatoes are.
If you aren't able to get beautifully ripe tomatoes, that's ok! You are cooking them way down with caramelized onions and added sugar, so they will get plenty sweet and the flavor will intensify.

Recipe FAQs

How do I store caramelized onion tomato jam leftovers?

Any leftovers can be stored in an airtight container in the fridge for up to one week.

Can I freeze this tomato jam?

Yes, you can also freeze this tomato jam! I froze some for later and didn't notice any loss in quality or texture from the freezing process. Just freeze the jam in an airtight container for 3 - 4 months, and then thaw in the fridge prior to serving.

How do I serve this tomato jam?

As I mentioned earlier, this caramelized onion tomato jam tastes great on so many things! I've heaped it on top of home fries and served it with eggs for breakfast. For lunch, spread it on bread for a grilled cheese sandwich, or use in place of ketchup on a burger.

It also makes a great addition to an appetizer spread, with a cheese plate, charcuterie, or on crostini with a smear of whipped cream cheese or slice of soft cheese.

onion tomato jam and cheese on crostini on marble board

tomato salad on platter with serving spoon — **Creamy tomato cucumber salad**

side view of ricotta mushroom crostini on white platter — **Ricotta mushroom crostini**

marinated mozzarella balls in green bowl with fork — **Marinated mozzarella balls**

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Caramelized Onion and Tomato Jam

Print Recipe

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5 from 2 reviews

This caramelized onion and tomato jam recipe is the perfect accompaniment for a cheese plate, potatoes, or sandwiches. The balsamic vinegar gives the jam a subtle tanginess that complements the sweet onion and tomato flavors.

Author: Kate
Prep Time: 10 minutes
Cook Time: 1 hour 15 minutes
Total Time: 1 hour 25 minutes
Yield: 2 cups 1x
Category: Sides
Method: stove top
Cuisine: American

Ingredients

Scale

1 tablespoon olive oil
1 large onion or 2 small onions, thinly sliced (see note 1)
1 teaspoon salt (or to taste), divided
2 pounds tomatoes, about 6 - 7 medium vine tomatoes
3 tablespoons granulated sugar, or to taste (see note 2)
3 tablespoons balsamic vinegar

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Instructions

Heat olive oil in a large skillet on low heat.
Add thinly sliced onions to the pan and sprinkle with about ½ teaspoon salt.
Distribute onions in an even layer in the pan. Cook until onions are deep golden brown, about 40 - 45 minutes. Stir occasionally.
While onions are cooking, prepare the tomatoes. Cut the stem out of each tomato and cut in half horizontally. Scoop out the seeds and pulp from each tomato and dice.
When the onions are caramelized, turn the heat on the pan up to medium low. Add the tomatoes, balsamic vinegar, sugar, and remaining ½ teaspoon salt. Scrape up any brown bits that have formed on the bottom of the pan.
Cook, stirring occasionally, until the tomatoes begin to break down, have thickened and lost most of their moisture, about 30 minutes. (As the tomatoes lose their moisture during cooking, you may need to turn the heat back down to low to keep the mixture from burning.)
Taste the jam and add more salt if needed. Likewise, you can also add another splash of balsamic vinegar for extra tang, or another sprinkle of sugar to make the jam a bit sweeter. If you added additional vinegar and/or sugar, allow the mixture to continue cooking for another minute or two for the ingredients to incorporate.
Serve immediately with your favorite dish or keep in a sealed container in the fridge for up to 1 week.

Notes

I like using a sweet variety of onion, but any type will work. Red onions give a very nice deep color to the jam!
For my taste, 3 tablespoons of sugar yields a jam that tastes sweet, but not too overpowering. You can customize the sweetness level to your tastes. For a less sweet jam, start with 1 - 2 tablespoons sugar. You can taste the jam during cooking and add more if needed.
After the deep golden brown stage for the onions has been reached, feel free to continue cooking the onions on low for even longer. They will continue to caramelize and develop even more flavor!
You can also freeze the jam in an airtight container for 3 - 4 months.

Caramelized Onion Tomato Jam