Preheat oven to 275 degrees F. Grease and flour 9X13-inch cake pan.
Mash bananas and mix with lemon juice. Set aside.
In large bowl, cream together butter and sugar with electric mixer. Add eggs and vanilla. Mix well.
Mix in half the flour, the salt and baking soda. Add in half the buttermilk. Repeat, mixing only until combined.
Gently stir in bananas. Pour into prepared pan.
Bake at 275 degrees F for 1 hour and 10 minutes to 1 hour and 30 minutes, or until a toothpick inserted into the center of cake comes out with only a few moist crumbs.
After baking, immediately place cake in freezer for 45 minutes then remove and let cool completely on the counter before frosting.