Cream 1/2 cup of the butter with the powdered sugar and cold water
Add egg yolks, cinnamon, flour, and baking powder; beat until combined.
Stir in the coarsely chopped walnuts
Gently fold in the stiffly beaten egg whites
Put the resultant batter in a well greased loaf pan and bake at 350 degrees for 40 to 45 minutes until a tooth pick inserted comes out clean
While the cake is baking beat or whisk the remaining butter in a large bowl until soft.
Add half of the icing sugar and beat until smooth.
Add the remaining icing sugar and one tablespoon of the milk and vanilla extract and beat the mixture until creamy and smooth. Beat in the remaining milk, if necessary, to loosen the mixture.
After the cake is out let it cool for 20 minutes in the refrigerator or counter cool for 35 minutes before glazing with the icing
Sprinkle with the finely chopped remaining walnuts
Serve in place of coffee cake. Great hot or cold