Cut the bacon and fry it in the pot with a little bit of butter. Wait until it starts to release fats. Put chopped onions and cook for about 5 minutes. Put finely chopped garlic and cook for another five minutes. Pour the broth, tomatoe paste, chopped tomatoes, sauce, and chili powder. Put the beans and wait until everything boils. Reduce temperature and boil in an open pot for about 15 minutes.
Before serving, add a spoon of sour cream and a slag of lemon juice. If you want, you could also grate some cheese.
An Observation: You can serve it as a side dish as well as the main course.