Preheat the oven to 275°F (135°C). Grease and flour a 9×13-inch baking pan.
In a small bowl, mix the mashed bananas and lemon juice. Set aside
Combine flour, baking soda, and salt in a separate bowl.
In a large mixing bowl, cream together the butter and sugar until fluffy. Beat in the eggs one at a time, then stir in vanilla.
Gradually add the dry ingredients and buttermilk to the creamed mixture, alternating. Fold in the banana mixture.
Pour the batter into the prepared pan. Bake for 1 hour or until a toothpick inserted into the center comes out clean.
Remove from the oven and place immediately in the freezer for 45 minutes.