Preheat oven to 350 degree F. Grease two 9-inch cake pans with shortening and flour. I like to use these Wilton's Bake Even Strips. It keeps your cake layers level and flat, perfect for stacking (and the just slide right onto your cake pans)! Set aside.
In a large mixing bowl, beat butter and sugar until creamy, about 3 minutes. Add in egg, vanilla, and bananas (you can mash them first, but I toss them in and it does the work). Add in flour, baking powder, baking soda, salt, and cinnamon. Beat for a couple minutes until fully blended.
Pour batter evenly between the two cake pans. Bake for 25 minutes. Remove from oven and cool in pans for about 10 minutes. Flip onto a cooling rack to cool completely before frosting.
For the frosting, beat butter and cream cheese for 3-4 minutes, until light and fluffy. Add in vanilla, heavy cream, and powdered sugar. Beat an additional 3-5 minutes. scraping down the sides of the bowl periodically. Beat in 1 teaspoon of cinnamon if you want a cinnamon spice frosting.
To assemble the cake, lay one layer of cooled cake on a cake plate. Spoon frosting over middle layer generously. Top with second layer of cake. Spoon and spread frosting over cake evenly. ENJOY!
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Notes
Ensure that your butter (and cream cheese for the frosting) are room temperature.
Don't over mix the cake batter. When adding the dry ingredients, do it just until combined.
Check your oven temperature for accuracy. Oven temps oven vary, so if you don't have a gauge in your oven, be sure to check your cake early.
Use Wilton's bake even strips. They wrap around your cake pan and create LEVEL cakes which results in NO waste.