Small cakes:
Preheat the oven to 350 F (180 C).
Line a 12-muffin tin with paper liners.

In a bowl, mix the pureed bananas, buttermilk, melted butter, egg, and vanilla extract. Set aside.
In another bowl, combine the flour, cinnamon, baking powder, baking soda, and salt.
Add the wet ingredients to the dry ingredients and mix with a fork, just until the dry ingredients are moistened.

Divide the batter evenly among the liners, and bake for 20 minutes.
Let the cakes cool completely on a wire rack.

Once the cakes are cool, put the jam in a piping bag with a pointed tip.
Make a hole in the top of each cake and fill with about 1 tablespoon of jam, inserting the tip almost to the bottom of the cake.

Glaze: With an electric mixer, cream the butter and peanut butter.
Add the vanilla, then the powdered sugar, alternating with the milk.
Mix until the mixture is smooth and fluffy.
Put the mixture in a piping bag with a fluted tip and frost the cakes.