Preheat oven to 350 degrees F (175 degrees C). Grease a large cookie sheet.
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. Place onto the prepared baking sheet. Sprinkle the top with a mixture of 2 teaspoons sugar and cinnamon.
Bake for 50 to 55 minutes in the preheated oven, until a toothpick inserted into the center, comes out clean.