Wash tomatoes thoroughly.

To peel: Bring a large pot of water to a boil. Score the bottom of each tomato with an “X” and blanch in boiling water for 30–60 seconds until skins loosen.

Transfer to an ice bath, then peel and core the tomatoes.

In a large stockpot, heat olive oil over medium heat.

Sauté chopped onion until soft (about 5 minutes), then add garlic and cook for another minute.

Add peeled and chopped tomatoes.

Simmer uncovered for 45–60 minutes, stirring occasionally, until tomatoes break down and mixture thickens.

Use an immersion blender for a smooth texture or pass the mixture through a food mill to remove seeds and skins.

Stir in salt, sugar, and any desired herbs. Simmer for another 20 minutes to let flavors meld.

Taste and adjust seasonings as needed

While the sauce simmers, sterilize jars by washing them in hot, soapy water and placing them in boiling water for 10 minutes.

Keep jars hot until ready to use.

Heat lids in a small pot of simmering water (do not boil).

To ensure safe acidity levels, add 2 tablespoons of bottled lemon juice to each pint jar (4 tablespoons for quarts).

Using a funnel, ladle hot tomato sauce into jars, leaving ½  inch headspace.

Wipe rims with a clean damp cloth to remove residue.

Place lids on jars and screw on bands until fingertip-tight.

Place jars in a boiling water bath canner. Ensure jars are covered by at least 1 inch of water.

Process pint jars for 35 minutes and quart jars for 40 minutes.

Start timing when the water returns to a full boil.

Carefully remove jars using a jar lifter. Place on a towel and let cool undisturbed for 12-24 hours.

Check seals: lids should not flex up and down when pressed.

Label and store in a cool, dark place for up to 18 months.