Preheat oven to 350 degrees. Spray 2 – 8-inch round pans with non-stick spray.
In a large bowl, using a hand mixer or the bowl of a stand mixer fitted with paddle attachment, mix together the sugar, butter, eggs, and vanilla extract until well combined. Set aside.
1 cup granulated sugar, ¾ cup unsalted butter, 3 large eggs, 1 teaspoon vanilla extract
In another bowl, whisk together the flour, baking powder, baking soda, cinnamon, and salt. Set aside.
2 ½ cups all-purpose flour, 1 teaspoon baking powder, ½ teaspoon baking soda, 1 1/2 teaspoons ground cinnamon, ½ teaspoon kosher salt
In a small bowl, using a fork, mash the bananas until most of the big chunks are gone.
2 large (or 3 medium) overripe bananas
Combine the flour mixture, bananas, and the buttermilk with the wet mixture. Mix until combined.
¾ cup buttermilk
Divide the batter evenly between the two prepared pans. Bake for 30-35 minutes, or until a toothpick inserted into the center of the cake comes out clean. Cool for a few minutes in the pan then turn layers out onto a cooling rack. Cool completely before preparing the frosting.