Ingredients:
3/4 cup butter
2 1/8 cups white sugar
3 eggs
2 teaspoons vanilla extract
3 cups Self Rising Flour*
1 1/2 cups buttermilk
2 teaspoons lemon juice
1 1/2 cups mashed bananas

Directions:

Preheat oven to 275 degrees F (135 degrees C).
Grease and flour one 9x13 inch pan or 2 8x3.
In a medium bowl sift the flour
Mix mashed bananas with lemon juice
Cream 3/4 cup butter and 2 1/8 cups sugar until light and fluffy.( around 10 minutes)
Beat in the eggs one at a time, then stir in 2 teaspoons vanilla.
Beat in the flour alternately with the buttermilk.
Fold in banana mixture with the batter.
Pour batter into pan
Bake in preheated oven until a toothpick inserted into the center of the cake comes out clean.
Remove from oven and wrap it in Plastic wrap before it cools down completely This will make the cake very moist.
 

* If you want to use regular flour instead of Self Rising use this instead.

Ingredients:
3/4 cup butter
2 1/8 cups  white sugar 
3 eggs
2 teaspoons vanilla extract
3 cups all-purpose flour
1-1/2 tablespoons baking powder
1/4 teaspoon salt
1 1/2 cups buttermilk
2 teaspoons lemon juice
1 1/2 cups mashed bananas