I had leftover sweet potato filling and pie crust (don't ask from when) in the freezer, and really wanted to use it up. Wasting food makes me sad, and eating food makes me happy, so obviously this 30-minute adventure was a win-win.
Pies in pictures:
I used a dip bowl from Crate and Barrel as the circle-cutter, and they fit into the muffin tins perfectly.
They puffed up quite a bit, but then fell when they cooled.