Place split peas in a heavy bottomed stock pot with two quarts of either water or broth. Bring to a boil, then turn to low and simmer gently for 1 hour until the peas are completely cooked.
(Optional) For a smooth soup, puree in a blender or with an immersion blender.
Peel and slice the carrots, and peel and dice the onions. Measure out 1 1/2 cups sliced carrots and 1 cup diced onion. Add to the pot.
Add the spices, either those listed in the recipe or dry spices of your choosing.
At this point, you're 30 minutes away from canning, so prepare your pressure canner and pre-heat it for hot pack canning. (Follow manufacturers instructions.)
Simmer the soup for an additional 30 minutes until the vegetables are fully cooked. (Add boiling water as nessisary to keep the mixture from getting too thick.)
Adjust spices and add salt to taste. Remove the bay leaf at this point, if used.
Ladle the split pea soup into prepared canning jars, either pints or quarts, leaving 1 inch headspace.
Seal with 2 part canning lids to finger tight.
Load the jars into the canner and close the lid. 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 75 minutes for pints and 90 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 split pea 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.