Smitten Kitchen has a great, great recipe for a no-fuss black bean soup. There's no need to mess with perfection, so here it is! (For those of you who don't have a slow cooker, you can make the soup without too much fuss in a pressure cooker.)
But because it you're not in the US, finding sour cream can sometimes be an issue, so I'm going to pass on my little tip. Use citric acid, which in Rio can be found at bulk retailers such as Casas Pedro. It is a white powder that looks like granulated sugar. I used about a half teaspoon for a half box of creme de leite (plus salt and toasted coriander seeds), and started stirring. And it just got thicker...and thicker...
