The riper the bananas in this recipe, the better. I'm a notorious banana hoarder (or a terrible banana eater?) -- I have nearly an entire freezer drawer full of them -- so my favorite way to get a silky, almost caramel flavor from the bananas in this recipe is to use defrosted frozen bananas. Freeze them whole, then defrost them in the peel. They'll end up dark, dark brown, and the fruit will be delightfully slimy and slug-like (when it's time to bake, let them slip from the peel right into the bowl) but I promise they make for the most decadent muffins.