Step 1

Quarter tomatoes and dice the onion. Place them in a large soup pot along with ½ cup of water. Cook, uncovered, for 30 min - 1 hour, stirring occasionally, until tomatoes are very soft.

Step 2

Remove tomatoes from the heat and let them cool slightly. Working in batches, transfer the warm tomatoes to a food processor, blender, or food mill to puree. If desired, press the tomato puree through a fine-mesh sieve to remove any seeds and skins.

Step 3

Pour the smooth tomato puree back into the large soup pot. (Using a very wide-bottomed pot will give you more surface area as you reduce tomatoes, making the process take less time.)

Step 4

Add the tomato paste, sugar, herbs, and spices. (Everything EXCEPT the lemon juice or citric acid.)

Step 5

Bring seasoned tomato puree to a simmer. Cook tomato soup until it has reduced to the thickness you desire. (Mine took 1 hour of simmering.)

Step 6

While the soup is simmering, wash canning jars and keep them warm. Prepare the water bath canner.

Step 7

When the soup has reached the desired thickness, taste it and adjust salt as desired.

Step 8

Add 1 Tbsp of lemon juice to each pint jar or 2 Tbsp lemon juice to each quart jar. (Or ¼ tsp citric acid to each pint and ½ tsp citric acid to each quart.)

Step 9

Fill jars with the soup, leaving ½ inch of headspace. (I like to use a canning funnel to reduce spills and messes.)

Step 10

Wipe the rims clean of any spilled soup. Then cover the jars with fresh lids and rings.

Step 11

Process your canned tomato soup in a boiling water bath canner for 40 minutes for pints or quarts. (Adjust the processing time as needed for your altitude.)

Step 12

After processing, carefully remove the jars from the water and set them on a cooling rack.

Step 13

Once the jars and soup have cooled, remove the rings and check that your lids have sealed.

Step 14

Finally, store the sealed jars in a cool place for up to a year. If any jars didn’t seal properly, refrigerate them immediately and eat within a week.