Preheat oven to 350 Â°F.
Grease 8-inch baking pan.
Add sugar; beat until light and fluffy.
Add eggs; beat until mixture is smooth.
Gradually add flour and salt sifted together.
Stir in nuts and vanilla.
Pour half the batter into pan.
Mix chocolate with other half of batter; pour over plain batter.
Swirl through with spoon.
Bake 30 minutes.
Cool; mark into squares or bars.
Cut when cold.