Preheat oven to 375ºF. Grease and lightly flour two 9” round cake pans.
Combine flour, salt, baking powder, and baking soda in medium bowl; set aside.
In a large bowl beat sugar and butter with an electric mixer until light and fluffy. Add eggs, one at a time, beating well after each addition. Blend in bananas.
Add flour mixture alternately with buttermilk, beating well after each addition. Stir in walnuts. Pour evenly into prepared pans.
Bake 30-35 minutes or until toothpick inserted in center comes out clean. Cool in pans on wire racks 10 minutes. Loosen edges, invert layers onto racks to cool completely before icing.
Frosting: Combine flour and salt in medium saucepan. Gradually stir in milk until well blended. Cook over medium heat until thickened, stirring constantly; cool. In a medium bowl beat butter until creamy. Add sugar; beat until light and fluffy. Blend in vanilla. Add flour mixture and beat until smooth.
Fill and frost cake layers with Frosting.
Optional: run a cake comb across top and around side of cake for a ridged effect.