Mash the bananas in a small bowl and mix with lemon juice
Sift the flour, baking soda, and salt in a medium bowl and set aside
In a large mixing bowl, cream the butter and sugar until light and fluffy using an electric mixer or stand mixer
Add in the eggs, one at a time, then the vanilla extract
Mix in the flour and buttermilk, a little at a time, alternating between the two
Stir in the mashed bananas
Pour the batter into the cake pan(s) and bake for about one hour, until a toothpick comes out clean (cook time will vary based on the size of the cake pan used)
Remove from the oven and cool on a wire rack
Frosting
When the cakes are completely cool and ready to frost, cream butter and cream cheese together with an electric mixer or stand mixer
Beat in the vanilla extract
Slowly add the powdered sugar while mixing on low speed
Set the mixer to high speed and mix until the frosting is smooth, scraping the sides of the bowl as needed
Frost the cake as desired
Decorate with extra sliced bananas and sprinkles if desired