Preheat oven to 350 degrees. Grease two 8 inch pans, and dust with flour. In a small bowl, whisk together flour, soda, and salt. Cream butter or margarine and sugars. Beat in eggs, one at a time. Mix in the bananas. Add flour mixture alternately with the buttermilk to the creamed mixture. Mix only to combine, and not too much. Stir in the nuts. Pour batter into the prepared pans. Bake for 30 minutes. Remove from oven, and place on a damp tea towel to cool. Transfer to a cake plate, and frost with chocolate frosting or cream cheese frosting.