Place the chicken breasts in the bottom of a large stock pot, sprinkle with a handful of guascas, and add water. Bring to a boil and cook until the meat is tender. Remove chicken and set aside. Cover with foil and keep warm.
Add the potatoes and bring to a boil. Reduce heat and simmer, covered, for at least a couple hours, 4 hours is best. The yellow potatoes should start to break up in the soup, but if not, you can help the soup along by mashing some of the yellow potatoes in the pot.
Once the cooked chicken is cool enough to handle, remove the skin and bones. Cut the meat into small pieces and drop them back into the pot.
About 5 minutes before serving, add the remaining guascas and let it cook for 5 minutes, then serve.
Serve in deep bowls, making sure that each bowl gets some chicken and a piece of corn on the cob. Garnish with a dollop of heavy cream, capers, and cilantro leaves. You can eat the avocado on the side with the rice, or you can cut a slice into pieces and drop into your soup bowl. (I like the avocado chunks in my soup.)