Preheat the oven to 350 degrees F.
Grease or spray with commercial cooking and baking spray a rectangular pan, (Or glass dish) 13x9x2 inches
In a medium bowl, combine the cocoa and the baking soda.
Blend in ⅓ C melted margarine or butter.
Add the boiling water and stir until the mixture thickens.
Stir in the sugar, eggs and remaining ⅓ C melted margarine or butter until smooth.
Add the flour, vanilla and salt. Blend with a spoon until completely combined, but don’t over stir. Batter may still be slightly lumpy.
Stir in the 1 C chocolate chips and the walnuts (if desired)
Pour into the prepared pan
Bake for 35 to 40 minutes or until brownies begin to pull away from the side of the pan. Do not overcook brownies, you want them to be soft and chewy. Cool completely in the pan before putting on the mint layer.