This Slow Cooker Tomato Sauce, simply flavored with basil, onion and butter, is an easy, hands-off way to make a really flavorful sauce for pasta (and lots of other dishes too).

Regardless of what you called it at home, whether it be gravy, red sauce, marinara, or spaghetti sauce if you are an Italian-American, like me, you likely grew up with something like this simmering away on a Sunday morning. And there are very few smells that make me feel nostalgic quite like the smell of Sunday sauce. This recipe, which is much different than the one I had growing up, is my version.

It is infinitely inspired by Marcella Hazan's famous tomato sauce. I first learned of that simple, yet profound butter and onion tomato sauce about a decade ago, and this recipe is my take on it. Over the years I've tweaked it to fit my own preferences, adding a bit more spices and herbs, as well as a pinch of sugar. At some point, I also started cooking it in the slow cooker all day, and it was a revelation. The slow simmer of it really transforms the flavor into something special.

This Slow Cooker Tomato Sauce is well-balanced, super flavorful, and incredibly smooth tasting without much acidity. Plus, it's made simply in the slow cooker with really no hands-on cooking time.

Ingredients for slow cooker tomato sauce.

Ingredients and Substitutions

Here is a brief overview of the ingredients needed for this recipe. The full recipe with quantities is listed below this text in the recipe card. If substitutions are available for this recipe, they'll be listed here. If you don't see a substitution you are looking for, please leave a comment below.

whole peeled San Marzano tomatoes (see note)
onion
butter
turbinado sugar (I love the flavor this sugar adds to it, but regular granulated sugar can be used if needed)
kosher salt
garlic cloves
dried oregano
fresh basil

Ingredients for tomato sauce in a slow cooker.

Why San Marzano Tomatoes?

This recipe calls for San Marzano tomatoes. This is simply because they lend the best flavor to this recipe as far as canned tomatoes are concerned. This recipe is so easy, except for this small instruction of calling for a very specific type of tomato. They are worth the effort to seek out and buy for this recipe.

Can you make this recipe without canned San Marzano? Sure, it just won't be as good.

The one exception to this is if you are using homegrown or farm heirloom tomatoes. And you certainly can use those for this recipe, just be sure to remove the skin and stem from them before using them in this recipe.

A jar of tomato sauce made in the slow cooker.

Why the Slow Cooker is the Best Tool for this Recipe

Not only is using the slow cooker a good choice for making dinner (for all the obvious reasons) but it also is key to the deep flavor of this tomato sauce recipe. The low and slow simmer of the tomato sauce with the butter and onion really helps to soften the acidity just enough, while enhancing the tomato flavor. It's a truly smooth and enjoyable tomato sauce.

One minor note about different types of slow cookers in regards to evaporation. Some slow cookers I've seen have a snap on the lid to make it a very tight seal. While this may be good for some recipes, it isn't for this recipe. The tomato sauce in this recipe is enhanced by some natural evaporation during the cooking process. So if your lid has those snaps, and you are able to, don't tighten them while the sauce cooks.

A bowl of pasta with tomato sauce made in the slow cooker.

Storing Tomato Sauce

This tomato sauce will keep in the refrigerator for about 5-7 days and it freezes really well.

Glass mason jars work really well for storage, especially for freezing. Just be sure to leave some room at the top for expansion.

And if you didn't know this, tomato sauce has a lot of acidity in it so don't ever leave tomato sauce in an unlined metal container for an extended period of time. It will react with the metal and taint the sauce.

Making the recipe? Be sure to leave a comment with a star review on your experience! Have a question? Leave a comment below and I’ll get back to you as quickly as I can!

Full Recipe

Slow Cooker Tomato Sauce

5 Stars 4 Stars 3 Stars 2 Stars 1 Star 5 from 2 reviews

Author: Kelli Avila
Prep Time: 00:05
Cook Time: 08:00
Total Time: 8 hours 5 minutes
Yield: 1-½ quarts 1x
Method: Slow Cooker

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Description

This Slow Cooker Tomato Sauce, flavored simply with basil, onion and butter, is an easy, hands-off way to make a really flavorful sauce for pasta (and lots of other dishes too).

Ingredients

Scale

2 (28 ounce) cans san marzano tomatoes
4 tablespoons butter
1 medium onion, peeled but left whole
2 cloves garlic
1 tablespoon kosher salt, more to taste
1 tablespoon turbinado sugar
3 sprigs of fresh basil
1 teaspoon dried oregano

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Instructions

Add all ingredients, to a large slow cooker and cook on high for 4-6 hours or low for 6-8 hours.
Once done, remove the onion, garlic cloves and basil and discard.
If desired, break up the tomatoes with a potato masher, or you can partially or fully puree the tomato sauce.
Taste and adjust the seasoning, adding more salt when necessary.
Serve as desired.

Notes

Why specifically San Marzano tomatoes? Simply because they offer the best flavor for this simple tomato soup using canned tomatoes. Most grocery stores will sell canned San Marzano, so be sure to grab them if you can to use in this recipe.

If your slow cooker has a tight fighting lid that prevents any evaporation, if you are able to, do not snap the lid closed. It’s best if the lid isn’t very tight fitting to allow some minor evaporation to occur.