Preheat oven to 180 degrees C. Grease a large baking tray.
In a large bowl, cream together the 2 cups sugar and margarine until smooth. Beat in eggs one at a time, mixing well after each one. Combine the cake meal, potato starch and salt; stir into the creamed mixture. Mix in walnuts and chocolate chips. The mixture will be heavy.
Form into 2 long oval loaves and place on the baking tray. Sprinkle the top with a mixture of 2 teaspoons sugar and cinnamon.
Bake for 50 to 55 minutes, until a toothpick inserted into the centre comes out clean.