Yep, that's right, sour cream on a pizza. Or were you perhaps more concerned about the beans? Well I assure you, both were wicked good. Unfortunately this was done on a whim and with various leftovers so I don't have anything approaching a recipe for it, but I can tell you basically what I did.
I had made the beef and beans some time ago and had a little bit leftover that I had frozen. What it was was a couple pieces of seared steak tips that was leftover from something else (heh, this is like a third generation pizza) which I cut up into smaller chunks, then I tossed a can of beans (pinto, I believe and rinsed of course) a bit of chicken broth and some Mexican seasonings (cumin, cayenne, cilantro, oregano, garlic, onion, etc) in a pot and let it simmer for several hours, until the beef was shreddable. Then I shredded it and at the time we just scooped it up with tortillas.
Like I said, I froze the bit that was leftover and one day decided to make a pizza out of it. To add a bit of something different I decided to dollop some sour cream on there and it worked out really well. The little bursts of tangy sour cream went perfectly, although not surprisingly, with the spicy beans and beef and the whole thing just came together really well. While I can't give you a specific recipe (yet, that is) I strongly recommend trying out the concept, it was a lot of fun and wicked good.