Preheat oven to 180 degrees C. Grease and flour a cake tin or pudding mold.
In a bowl, beat the sugar with the melted butter, egg yolks, lemon zest and port.
Sift together the flour, pinch salt and baking powder. Add it to the mixture alternately with the milk. Stir in the raisins and walnuts. Finally, beat the egg whites until soft and carefully stir in.
Pour the batter into the tin and bake 45 minutes or until a knife tests clean.