Preheat your oven to 350°F (175°C). Grease and flour a 9x13-inch baking pan.

In a medium bowl, whisk together the flour, baking soda, salt, and cinnamon. Set aside.

In a large mixing bowl, cream the softened butter and granulated sugar together with an electric mixer on medium speed until the mixture is light and pale, approximately 2-3 minutes.

Beat in the eggs, one at a time, followed by the mashed bananas, scraping down the bowl as needed.

Add the dry flour mixture to the wet ingredients in three parts, alternating with the buttermilk in two parts, beginning and ending with the flour. Mix on low speed after each addition until just combined.

Pour the batter into the prepared pan and spread it evenly. Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean. Let the cake cool completely in the pan on a wire rack.

In a clean mixing bowl, beat the softened cream cheese and butter together until completely smooth and creamy. Mix in the vanilla extract.

Gradually add the powdered sugar with the mixer on low speed, increasing to medium-high once incorporated, and beat until the frosting is fluffy.

Spread the frosting evenly over the completely cooled cake. For a marbled effect, use the tip of a knife or an offset spatula to create gentle swirls in the frosting. Slice and serve.