Because you blend part of the cooked pintos with crushed tomatoes, the base of the soup is very creamy, like adding refried beans to a pot of whole beans. The spiciness comes from canned chipotle chilies in adobo sauce, and although the recipe called for one teaspoon, I doubled this, as we like our food spicy. I would test this out first if you aren't familiar with the type of heat provided by chipotles. They are hot, with a hint of smokiness, but again, they are HOT!
The recipe calls for four cups of broth or water; I used the left over cooking liquid from the beans for this, adding depth of color and extra flavor to the soup. And, the only change I made to make this recipe McDougall friendly was to "dry fry" the onion instead of sautéing in oil.