In a deep sauce pan on medium heat, sauté the onion and garlic in olive oil, until transparent, about 5 minutes.
Add the tomatoes and salt to taste.
Let it boil for 5 minutes and then lower the heat.
Add the herbs and let simmer, uncovered, for 30 minutes.
Discard the herbs.
Blend the sauce with an immersion blender.
If you don’t have an immersion blender, let the sauce cool down and process it in a conventional blender.
Pour the sauce in sterilized jars. Make sure to leave ½ -inch headspace and that there is no food or juice in the headspace (food particles may interfere with sealing). Cap the jars for processing by fitting a screw band snugly over the jar rim and lid.
Fill a water bath canner halfway with water. Place the jars in the rack. Make sure the water covers the jars at least by 1 inch. Cover the canner and bring the water to boil. Once the water starts boiling, process for 20 minutes (6 ounces jars) or 30 minutes (1 pint jars).
Place the processed jars on kitchen towels. Let them rest until they cool down. The lids will pop and become concave, indicating the jars are sealed. If the lid doesn’t pop and doesn’t look concave, reprocess the jar with a new lid or refrigerate and eat in the next few days.
Canned tomato sauce must be saved in a dark place.