Beat egg whites to stiff but moist peaks. Combine flour, baking powder, salt and spices in a large mixing bowl. Stir well to blend. Add butter, sugar, egg yolks, milk and vanilla. Beat with electric mixer on medium speed until smooth, about 1 1/2 minutes. Stir in raisins. Fold in stiff egg whites.
Spread batter evenly in greased 9 " square cake pan.
Bake at 375 degrees F. for 30 - 35 minutes. Cool completely.
Icing: Cream butter, half of icing sugar and lemon juice together until light. Gradually add icing sugar and enough cream to make a smooth spreading consistency. Spread over cooled cake. Sprinkle with chopped walnuts, to decorate, if desired.