Preheat your oven to 350°F (175°C). Grease and flour a 9x13-inch baking pan.
In a small bowl, mix the mashed bananas with lemon juice and set aside.
In another bowl, sift together the flour, baking soda, and salt. Set aside.
In a large mixing bowl, cream the butter and sugar until light and fluffy. Beat in the eggs one at a time, then stir in the vanilla extract.
Add the flour mixture to the butter mixture alternately with the buttermilk, beginning and ending with the flour mixture. Mix until just combined.
Fold in the mashed bananas and pour the batter into the prepared pan.
Bake for 45 minutes, or until a toothpick inserted into the center comes out clean. Allow the cake to cool completely in the pan.
For the frosting, beat together the butter and cream cheese until smooth. Gradually add the powdered sugar and vanilla extract, mixing until fluffy.
Spread the frosting evenly over the cooled cake. Serve and enjoy!