Preheat oven to 325 degrees Fahrenheit. Grease an eight- by eight-inch baking pan with nonstick cooking spray.

In a medium bowl, whisk together flour, baking soda and salt.

In a large bowl, use an electric mixer to combine sugars, applesauce, margarine, egg, egg yolk and vanilla. Beat until creamy.

Add the flour mixture to the large bowl, and beat to combine. Stir in chocolate chips and nuts (if using).

Spread mixture in pan and bake for about 25 minutes, or until a toothpick inserted into the center comes out clean.

Drizzle melted chocolate over the top of the cake.