Step 1

Heat the oven to 350° F.

Step 2

Cream together the butter and sugar, then one at a time, mix in the egg yolks, bananas, and sour milk, stirring after each addition until combined.

Step 3

In a separate bowl, whisk together the flour, baking soda, baking powder, and salt. Add the dry ingredients (and the nuts if using) to the wet ingredients and stir to combine.

Step 4

Beat the egg whites until soft peaks form, and fold into the batter.

Step 5

Butter and flour two 8-inch cake pans, divide the batter evenly between the pans, and bake for 25 to 30 minutes or until done.

Step 6

In a saucepan over low heat, melt the butter and stir in the brown sugar. Cook for 2 minutes, stirring constantly.

Step 7

Add the milk, raise the heat, and cook until the mixture boils. Remove from heat, and let it cool until the mixture is lukewarm.

Step 8

Gradually stir in the powdered sugar, beating until smooth.