This soup has a smokey heat to it that really distinguishes it from spicy Italian tomato soup. Paired with the cilantro and topped with avocado, you'll be surprised how tasty a simple five-ingredient tomato soup can be.
Prep work comes first. Cut one onion in half, chop into 1/4 inch pieces. Second onion, slice as thinly as possible. Wash and dry cilantro, collect 1/3 cup of loosely packed leaves and reserve. Peel avocado, cut into half-inch slices.
In a bowl, put thin slices of onion and avocado together and cover with lime juice. Make sure avocado is coated, use more lime juice if you have to.
Cut one large dried chipotle in half and remove stalk. Preferably with a food processor, dice and shred the pepper until you can measure out about one to two teaspoons of pepper.
In a large pot, add olive oil and heat to medium high. Add 1/4 inch chunks of onion and chipotle. Stir continuously until onions are translucent -- around 10 minutes.
Add both cans of whole tomatoes to pot, including their juices, and then fill up each can about 1/3 of the way with water, collecting the remaining tomato residue on the walls, and pour into pot. Add bay leaf.
NOTE: The kind and brand of tomatoes you use really makes a world of difference. You want to make sure you're using plum tomatoes, and I would suggest relying on tomatoes from the San Marzano region unless you can your own.
Bring uncovered pot to a roiling boil, and then reduce to low heat to allow contents to simmer together for 30 minutes. Stir occasionally.
Take pot off heat. Add salt, pepper, cilantro and stir in. Allow to sit and cool down for 5 minutes. Find and remove bay leaf.
In batches, add pot contents to blender. Blend until as smooth as possible.
Over a heat-resistant bowl, pour into mesh strainer and allow soup contents to strain through, using the back of a spoon to press and scrape contents against the mesh until small amounts of solids are left. Be sure to scrape the contents from the exterior of the strainer into to the soup bowl as well.
The consistency of the soup should be smooth, but thick -- not watery or chunky.
Return bowl's contents in a pot to the stove and heat up on low heat until warm enough to serve. Do not boil again.
Garnish with a few pieces of avocado and thinly sliced onion, and add a dollop of yogurt or sour cream if desired.