Preheat oven to 325 degrees.
In medium bowl mix egg, sugar, salt, vanilla and melted margerine.
In a seperate bowl, mix together cocoa and flour. Mix the cocoa mixture into the egg mixture. Stir well.
Spread batter into a 9 x 9 inch pan sprayed with nonstick cooking spray.
Bake for 30-35 minutes or until a toothpick inserted into center comes out clean.
Cool and cut. Store airtight for up to one week.