These are always moist and tasty! This was one of the recipes that convinced my boyfriend to become my husband 37 years ago.
The secrets to making these especially wonderful are make sure your bananas are so ripe they are black and having them mashed and frozen is even better, and make sure you freeze the muffins before you eat them so that their moisture distributes through the whole muffin.
TIP: The bananas at minimum need to have black spots on the peels but letting them ripen to all black is best since that is when they are at their sweetest. Since it is difficult to get the right amount of bananas ripe at the same time, peel and individually freeze them in a container until you get enough of them or enough time to make your muffins. Bananas that are black on the outside, mushy and slimy on the inside, or that have been frozen are perfectly fine to use in baking--they are not spoiled!