Preheat oven to 350°
Prepare an 8" round cake pan by lining the bottom with parchment paper or greasing the pan.
Smash one banana and set aside.
Whisk flour, baking powder, salt and cinnamon in a small bowl.
Place butter and granulated sugar in stand mixer bowl. Begin creaming the butter and sugar until light and fluffy (2 - 4 minutes), scraping bowl occasionally.
Add room temperature eggs, one at a time, scraping bowl between each addition. Mix on medium-low speed until eggs are well incorporated.
Add the rum and mix for approximately 30 seconds,
Add the smashed banana and mix for approximately 60 seconds.
Add the flour mixture and mix on low speed until just combined.
Pour half of the batter into the prepared pan. Slice 2 bananas in ¼" slices and layer on top of cake batter.
Pour second half of cake batter over bananas and smooth top with an offset spatula.
Sprinkle 2 tablespoons of granulated sugar evenly over top of cake.
Bake for 50 - 60 minutes at 350°. The cake top will be a golden color and a toothpick inserted in the center of the cake will come out clean when the cake is done.
Place cake on a rack and allow to cool completely before unmolding.
If desired, sprinkle confectioners' sugar over top of cake after unmolding.