1. Sift together sugar, flour and salt.
2. Add eggs and vanilla and mix well.
3. Stir in walnuts and melted margarine.
4. Pour into greased and floured 13 x 9 pan.
5. Bake at 350*, 35-40 minutes. Sprinkle immediately with 4 cups miniature marshmellows.
6. Drizzle with Butterscotch Icing.