Cake: Preheat oven to 180 degrees C. Grease and flour two 20cm round cake tins.
In a large bowl cream together the butter and white sugar until light and fluffy. Beat in the egg yolks one at a time. Dissolve bicarb soda in buttermilk then add to creamed mixture alternately with flour, beginning and ending with flour. Stir in the mashed bananas and pecans.
In a large glass or metal mixing bowl, beat egg whites until stiff peaks form. Fold 1/3 of the whites into the batter then quickly fold in remaining whites until no streaks remain. Pour batter into prepared cake tins.
Bake in the preheated oven for 30 to 35 minutes or until a toothpick inserted into the centre of the cake comes out clean. Let cool in pans for 10 minutes then turn out onto a wire rack and cool completely.
Caramel Icing: In a heavy saucepan, combine the white sugar, brown sugar, evaporated milk and butter. Cook over medium heat, stirring frequently, until mixture reaches soft ball stage (115 degrees C). Remove from heat and beat until spreading consistency. Add additional milk if necessary.
To Assemble: As soon as the caramel icing is ready spread immediately between layers, on top of and on the sides of the cooled cake.