Goofing Off with Maven

I downloaded Maven the other day, but I really haven't messed around with it too much. However, today I decided to try out the create a board feature. With it I can make up a position, and Maven will tell me what the best play is.

I tried to think of a position that might even stump the mighty Maven. But it came up with the answer in less than a blink of the eye.

In the following position, can you find the best play?

The rack is ABLMOU?.