Preheat oven to 375 F. Grease and flour 15×10-inch jelly roll pan.
Beat together sugar, buttermilk (or sour cream), butter, and eggs until creamy. Blend in bananas and vanilla. Add flour, baking soda, salt, and blend for 1 minute.
Spread batter evenly into pan. Bake 20 to 25 minutes or until golden brown.