Add egg yolks, one at a time, beating well after each addition.
Dissolve soda in buttermilk; add to creamed mixture alternately with flour, beginning and ending with flour.
Stir in mashed bananas and pecans.
Beat egg whites (at room temperature) until stiff peaks form; fold into batter.
Pour batter into 2 greased and floured 8 inch round cake pans.
Bake at 350 degrees for 30 minutes or until toothpick comes out clean.
Cool cake in pans 10 minutes; remove layers from pans, and let cool completely.
For frosting, combine all ingredients in a heavy saucepan; cook over medium heat, stirring frequently until mixture reaches soft ball stage (240 degrees).
Remove from heat, and beat until spreading consistency; add additional milk, if necessary.
Spread immediately on cooled cake between layers and on top and sides.