1. Start heating oven to 325Â°F.
2. Sift flour with salt and baking soda.
3. With hand beater or mixer, beat egg until foamy. Add brown sugar and vanilla; beat well. Stir in flour mixture, then walnuts. With spatula, spread mixture in well-greased 8-by-8-by-2-inch pan.
4. Bake 25 to 30 minutes, or until top has dull crust.
5. While still warm, cut into 16 2-inch squares; cool completely before removing from pan.