Cake - Devils Food Cake

1/2 cup butter                            
1 cup sugar                              
2 eggs                                        
1/2 cup sour milk                      
1 tsp baking soda
1 1/2 cups flour
1 tsp baking powder
6 heaping tsp cocoa
1/2 cup boiling water
1 tsp vanilla

Cream butter well.  Add sugar gradually.  Beat egg yolks until thick and add to creamed butter and sugar.  Sift all dry ingredients together.  Add dry ingredients and milk alternately.  Stir the batter only enough to make it smooth.  Mix cocoa into boiling water.  Add to batter and then add vanilla.  Stiffly beat the egg whites and then fold them into batter.

Pour batter into 13 x 9" pan and bake at 350 degrees for about 30 minutes.