Slice the fennel (or onion/celery), if using.
Saute the fennel in 1 Tbsp of olive oil until tender and translucent. (If using. You can also substitute celery or onion, but sautee them in this step as well.)
Peel and chop the carrots.
In a stock pot, add the water/stock, chopped carrots and sauteed vegetables. Bring to a boil and cook until tender, about 15-20 minutes. Turn off heat.
Puree the soup until smooth, using an immersion blender or regular blender. Be careful here, soup is hot.
Prepare the pressure canner at this point.
Return the pureed soup to the stock pot, and add salt and seasonings of your choice. Simmer for an additional 30 minutes, adjusting seasonings and adding boiling water if the soup gets too thick.
Ladle the soup into prepared jars, either pints or quarts, leaving 1 inch headspace.
Seal wth 2 part canning lids to finger tight.
Load the jars into your pre-heated pressure canner. Turn the stove up to high and vent steam for 10 minutes.
Seal the canner and bring it up to pressure. When at pressure (see notes below), start timer and process the jars for 40 minutes for pints and 50 minutes for quarts.
When the processing time is complete, turn off the heat and allow the canner to come to room temperature naturally.
When cool, remove the jars from the canner and check seals. Store any unsealed jars in the refrigerator for immediate use.
Properly pressure canned and sealed jars of carrot soup should
maintain quality on the pantry shelf for 18 months, and be safe to eat
much longer provided they're still sealed. Refrigerate after opening.