Preheat oven to 275°F. Grease and flour a 9 x 13 pan.
In a small bowl, mix mashed bananas with the lemon juice; set aside.
In a medium bowl, mix flour, baking soda and salt; set aside.
In a large bowl with an electric mixer, cream 3/4 cup butter and 2 cups sugar until light and fluffy; about 3 minutes. Beat in eggs, one at a time, then stir in 2 teaspoons of vanilla.
Beat in the flour mixture alternately with the buttermilk until just combined. Stir in mashed bananas.
Pour batter into prepared pan and bake in preheated oven for 60-75 minutes, or until toothpick inserted in center comes out clean. This could take longer than 75 minutes depending on your oven.
Remove from oven and place directly into the freezer for 45 minutes. This will make the cake extremely moist.
For the frosting, cream the butter and cream cheese until smooth. Add in 1 teaspoon vanilla and mix until incorporated.
Add powdered sugar and beat on low speed until combined, then on high speed until frosting is smooth.
Spread on cooled cake and devour!